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3:257 


ox   THE   ORIGIN   OF  SPEGIES. 


"  But  with  regard  to  tlic  luatcrial  world,  vfc  can  at  least  go  so  far  as  tliia 
— wc  can  perceive  that  events  are  brought  about  not  by  insulated  interpo- 
sitions of  Divine  power,  exerted  in  each  particular  case,  but  by  the  estab- 
lishment of  general  laws." 

Whewkll:  Bridjcwatcr  Treatise. 


"  The  only  distinct  moaning  of  the  word  '  natural '  is  slalnl,  Jixcel,  or 
tcllled ;  since  what  is  natural  as  much  requires  and  presupposes  an  intelli- 
gent agent  to  render  it  so,  i.  c.,  to  effect  it  continually  or  at  stated  times, 
as  what  is  supernatural  or  miraculous  does  to  effect  it  for  once." 


Butler  :  An(do<ji/  of  Revealed  Religion, 


"  To  conclude,  therefore,  let  no  man  out  of  a  weak  conceit  of  sobriety, 
or  an  ill-applied  moderation,  think  or  maintain,  that  a  man  can  search  too 
far  or  be  too  well  studied  in  the  book  of  God's  word,  or  in  the  book  of 
God's  works ;  divinity  or  philosophy  ;  but  rather  let  men  endeavor  an  end- 
less progress  or  proCcicncc  in  both." 


Bacon  :  Advancement  of  Learning. 


ON  ,  .     ^ 

THE  ORIGIN  OF  SPECIES 


MEANS  OF  NATURAL  SELECTION, 


PRESERVATION  OF  FAVORED   RACES  IN  THE  STRUGGLE 
FOR  LIFE. 


BY 

CHAELES    DAEWIN,  M.A.,   F.E.S., 

4VTII0P.  OP    "  JOUr.NAL  OF    lU-;8EAKCnES   DURING   H.    M.    S.   BEAOLE's    VOYAGE    KOUND 
TOE  WOnLD,"  ETC.,  ETC. 


Flinil    EPfTlOX,    WITH    ADDITIoyS    ASD    CORItECTIOXS. 


NEAV  YOEK: 
i>.    A  PPL  ETON    AND    COMPANY, 

5  4  9    &    5  5  1     BROADWAY. 
1871. 


OOISTTEIS'TS 


nisTORiCAL  Sketch     ........  paoe      9 

I.VTBOnUCTION  .........  17 

CHAPTER  I. 

VARIATION    CNDE.I    DOMESTICATION. 

Causes  of  Variability— EfTocts  of  Habit— Correlated  Variation— Inheritance— Char- 
acter of  Domestic  Varieties — Diflftculty  of  distinguishing  between  Varieties  and 
Species— Origin  of  Domestic  Varieties  from  one  or  more  Species — Domestic 
Pigeons,  their  Differences  and  Origin— Principles  of  Selection,  anciently  followed, 
their  Effects — Methodical  and  Unconscious  Selection— Unknown  Origin  of  our 
Domestic  Productions— Circumstances  favorable  to  Man's  Power  of  Selection   23 

CHAPTER  II. 

VARIATION    UNDER    NATCRE. 

Vailability- Individual  Differences— Doubtful  Species— Wide-ranging,  much  dif- 
fused, and  Common  Species,  vary  most— Species  of  the  Larger  Genera  in  each 
Country  vary  more  frequently  than  the  Species  of  the  Smaller  Genera— Many  of 
the  Species  of  the  Larger  Genera  resemble  Varieties  in  being  very  closely,  but 
unequally,  related  to  each  other,  and  in  having  Restricted  Ranges  .  52 

CHAPTER  III. 

STRUGGLE   FOR   EXISTENCE. 

its  bearing  on  Natural  Selection— The  Term  used  in  a  wide  Sense— Geometrical  rjutio 
of  Increase — Rai)id  Increase  of  Naturalized  Animals  and  Plants — Nature  of  tlio 
Checks  to  Increase— Competition  universal— Effects  of  Climate— Protection  fri)ni 
the  Number  of  Individuals— Complex  Relations  of  all  Animals  and  Plants  through 


6  CONTENTS. 

out  Nature— Strugiclo  for  Life  most  severe  hctwccn  Individuals  and  Varieties  of 
the  same  Species :  often  severe  between  Species  of  the  same  Genns— The  Rela- 
tion of  Organism  to  Organism  the  most  important  of  all  Relations  faoe  69 

CHAPTER  IV. 

NATURAL    PKLKCTION,    OR   THE    SrUVIVAL    OF   TIIK    FITTEST. 

Natural  Selection— its  Power  compared  with  Man's  Selection — its  Power  on  Char- 
acters of  trifling  Importance— its  Power  at  all  Ages  and  on  both  Sexes — Sexual 
Selection— On  the  Generality  of  Intercrosses  bi^tween  Individuals  of  the  same 
Species — Circumstances  fiivorable  and  unfavorable  to  the  Uesults  of  Natural  Se- 
lection, namely,  Intercrossing,  Isolation,  Number  of  Individuals — Slow  Action — 
Extinction  caused  by  Natural  Selection— Divergence  of  Character  related  to  the 
Diversity  of  Inhabitants  of  any  Small  Area,  and  to  Naturalization— Action  of  Nat- 
ural Selection,  through  Divergence  of  Character  and  Extinction,  on  the  Descend- 
ants from  a  Common  Parent — Explains  the  Grouping  of  all  Organic  Beings— Ad- 
vance in  Organization— Low  Forms  preserved — Objections  considered— Uniform- 
ity of  certain  Characters  due  to  their  Unimportance  and  to  their  not  having  been 
acted  on  by  Natural  Selection— Indefinite  Multiplication  of  Species— Summary. 

CHAPTER  V. 

LAWS    OF  VARIATION. 

Effects  of  changed  Conditions — Use  and  Disuse,  combined  with  Natural  Selection  ; 
Organs  of  Flight  and  of  Vision — Acclimatization — Correlated  Variation — Com- 
pensation and  Economy  of  Growtli — False  Correlations — Multiple,  Rudimentary, 
and  Lowly-organized  Structures  variable — Parts  developed  in  an  Unusual  Man- 
ner are  highly  variable:  Specific  Characters  more  variable  than  Generic:  Second- 
ary Sexual  Characters  variable — Species  of  the  same  Genus  vary  in  an  analogous 
Manner- Reversions  to  long-lost  Characters — Summary     .  .  .  137 

CHAPTER  VI. 

DIFFICULTIES    OF   THE    TIIEORV. 

Difficulties  of  the  Theory  of  Descent  with  Modification— Transitions— Absence  or 
Rarity  of  Transitional  Varieties — Transitions  in  Habits  of  Life — Diversified  Elal)- 
its  in  the  same  Species— Species  with  Habits  widely  diO'erent  from  those  of  their 
Allies— Organs  of  Extreme  Perfection — Modes  of  Traifsition — Cases  of  Difficulty 
— Natura  non  facit  saltum— Organs  of  small  Importance— Organs  not  in  all  Cases 
absolutely  perfect — The  Law  of  Unity  of  Type  and  of  the  Conditions  of  Existence 
embraced  by  the  Theory  of  Natural  Selection  ....  167 

CHAPTER   VII. 

INSTINCT. 

Instincts  comjiarable  with  Ilabils,  but  different  in  tlu-ir  Origin— Instincts  graduated 
— Aphides  and  Ants— Instincts  variable— Domestic  Instincts,  their  Origin— Nat- 


CONTENTS.  Y 

nral  lOBtincls  of  the  Cuckoo,  Ostrich,  and  Parasitic  Bees— Slave-making  Ants — 
Hive-bee,  its  cell-making  instinct— ChanKCs  of  In!<linct  and  Structure  not  neces- 
earlly  simultaneous— Difllcultics  of  the  Theory  of  the  Natural  Selection  of  In- 
stincts—Xeuter  or  Sterile  Insects— Summary  .  .  .  .  PAGE  201 

CHAPTER  VIII. 

innuiDisM. 

Distinction  between  the  Sterility  of  First  Crospoe  and  of  Hybrids— Sterility  various 
in  Degree,  not  universal,  affected  by  close  Interbreeding,  removed  by  Domesti- 
cation-Laws goveiTiing  the  Sterility  of  Hybrids- Sterility  not  a  special  Endow- 
ment, but  incidental  on  other  DilTerenccB,  not  accumulated  by  Natural  Selection 
— Causes  of  the  Sterility  of  First  Crosses  and  of  Hybrids— Parallelism  between 
the  Effects  of  Changed  Conditions  of  Life  and  of  Crossing— Dimorphism  and 
Trimorphism — Fertility  of  Varieties  when  crossed  and  of  their  Mongrel  Offspring 
not  universal— Hybrids  and  Mongrels  compared  independently  of  their  Fertility 
—Summary  .........  233 

CHAPTER  IX. 

ON    TIIK    IMrEIlFECTION   OF  THE    GEOLOGICAL   KECOP.D. 

On  the  Absence  oflntcrmediatc  Varieties  at  the  Present  Day — On  the  Nature  of  Ex- 
tinct Intermediate  Varieties ;  on  their  Number— On  the  Lapse  of  Time,  as  in- 
ferred from  the  Kjite  of  Denudation  and  of  Deposition— On  the  Lapse  of  Time  as 
estimated  by  Years- On  the  Poorness  of  our  Palcontological  Collections— on  the 
Denudation  of  Granitic  Areas— On  the  Interaiittence  of  Geological  Formations — 
On  the  Absence  of  Intermediate  Varieties  in  any  one  Formation— On  the  sudden 
Appearance  of  Groups  of  Species— On  their  sudden  Appearance  in  the  lowest 
known  Fossilifcrous  Strata— Antiquity  of  the  Habitable  Earth      .  .  2CC 

CHAPTER  X. 

ON   THE    GEOLOGICAL    SUCCESSION    OF   ORCLVXIC    BEINGS. 

Ou  the  Slow  and  Successive  Appearance  of  New  Species— On  their  Different  Rates 
of  Cliange— Species  once  lost  do  not  reappear — Groups  of  Species  follow  the 
same  General  Kules  in  their  Appearance  and  Disappearance  as  do  Single  Species 
— On  Extinction— On  Simultaneous  Changes  in  the  Forms  of  Life  throughout 
the  World— On  the  Affinities  of  E.\tinct  Species  to  each  other  and  to  Living  Spe- 
cles- On  the  State  of  Development  of  Ancient  Forms— On  the  Succession  of  the 
eamc  Types  within  the  same  Areas— Summary  of  preceding  and  present  Chapter 

293 

CHAPTER  XI. 

GEOGUAmiCAL    DISTRIUITION. 

PrcBont  Distribntlon  cannot  bo  accounted  for  by  Differences  In  Physical  Conditions 
— Importance  of  Carriers — Aflliiity  of  the  Productions  of  the  same  Continent— 


CONTENTS. 

Centres  of  Creation— Means  of  Dispersal  by  Changes  of  Climate  and  of  the  Level 
of  the  Land,  and  by  Occasional  Means— Dispersal  during  the  Glacial  Period- 
Alternate  Glacial  Periods  in  the  North  and  South     .  .  .  page  322 


CHAPTER  XII. 

GEOGllAnilC'AL    DISTRIBUTION' COUtinUcJ. 

Distribution  of  Fresh-water  Productions— On  the  Inhabitants  of  Oceanic  Islands- 
Absence  of  Batrachians  and  of  Terrestrial  Mammals— On  the  Relation  of  the  In- 
habitants of  Islands  to  those  of  the  nearest  Main-land— On  Colonization  from  the 
nearest  Source  with  subsequent  Modification— Summary  of  the  last  and  present 
Chapter 351 

CHAPTER  XIII. 

MUTUAL    AFFINITIES    OF   ORGANIC    BEINGS  :    MORPHOLOGY  :    EMBRYOLOGY :    RUDI- 
MENTARY   ORGANS. 

Classiflcation,  Groups  subordinate  to  Groups— Natural  System— Eules  and  Difficulties 
in  Classification,  explained  on  the  Theory  of  Descent  with  Modification— Classi- 
fication of  Varieties- Descent  always  used  in  Classification— Analogical  or  Adap- 
tive Characters— Affinities,  General,  Complex,  and  Radiating— Extinction  sepa- 
rates and  defines  Groups— Morphology,  between  members  of  the  same  Class,  be- 
tween parts  of  the  same  Individual— Embryology,  Laws  of,  explained  by  Varia- 
tions not  supervening  at  an  early  Age,  and  being  inherited  at  a  corresponding 
Age— Rudimentary  Organs  ;  their  Origin  explained— Summary    .  .  372 

CHAPTER  XIV. 

RECAPITULATION    AND    CONCLUSION. 

Recapitulation  of  the  Objections  to  the  Theory  of  Natural  Selection— Recapitulation 
of  the  General  and  Special  Circumstances  in  its  favor — Causes  of  the  General 
Belief  in  the  Immutability  of  Species— IIow  far  the  Theory  of  Natural  Selection 
may  be  extended- Efl"ects  of  its  Adoption  on  the  Study  of  Natural  History— Con- 
cluding Remarks    .........  412 


«» 


Instruction  to  Binder.— The  Diagram  to  front  page  114. 


An  Historical  Sketcu  of  the  Recent  Progress  of 
Opinion  on  tue  Origin  of  Species. 


I  WILL  here  give  a  brief  slcetch  of  the  progress  of  opinion  on  the  Origin 
of  Species.  Until  recently,  the  great  majority  of  naturalists  believed  that 
species  were  immutable  productions,  and  had  been  separately  created.  This 
view  has  been  ably  maintained  by  many  authors.  Some  few  naturalists,  on 
the  other  hand,  have  believed  that  species  undergo Tiiodification,  and  that 
the  existing  forms  of  life  arc  the  descendants  by  true  generation  of  pre- 
existing forms.  Passing  over  allusions  to  the  subject  in  the  classical 
writers,*  the  first  author  who  in  modern  times  has  treated  it  in  a  scientific 
spirit  was  Buffon.  But,  as  his  opinions  fluctuated  greatly  at  different 
periods,  and  as  he  does  not  enter  on  the  causes  or  means  of  the  transforma- 
tion of  species,  I  need  not  here  enter  on  details. 

Lamarck  was  the  first  man  whose  conclusions  on  the  subject  excited 
much  attention.  This  justly-celebrated  naturalist  first  published  his  views 
in  1801 ;  he  much  enlarged  them  in  1809  in  his  "  Philosophic  Zoologique," 
and  subsequently,  in  1815,  in  the  introduction  to  his  "Hist.  Nat.  des  Ani- 
maux  sans  Vcrtcbres."  In  these  works  he  upholds  the  doctrine  that  all 
species,  including  man,  are  descended  from  other  species.  He  first  did  the 
eminent  service  of  arousing  attention  to  the  probability  of  all  change  in  the 
organic  as  well  as  in  the  inorganic  world  being  the  result  of  law,  and  not  of 
miraculous  interposition.     Lamarck  seems  to  have  been  chiefly  led  to  his 

*  Aristotle,  In  his  "  Phygictc  Anecultationes  "  (I'l'-  2,  cap.  8,  s.  2),  after  remarking 
that  rain  docs  not  fall  in  order  to  make  the  com  grow,  auy  more  than  it  falls  to  gpoil 
the  farmer's  com  when  threshed  out  of  doors,  applies  the  same  arf::umcnt  to  orfrani- 
zaliou,  and  adds  (as  translated  by  Mr.  Clair  Grecc,  who  first  pointed  out  the  passaio 
to  me):  "-So,  what  hinders  the  different  parts  [of  the  body]  from  haviuii  this  merely 
accidental  relation  in  Nature  ?  as  the  teeth,  for  example,  grow  by  necessity,  the  front 
ones  sharp,  adapted  for  dividing,  and  the  grinders  flat,  and  serviceable  for  masticat- 
ing the  food  ;  since  they  were  not  made  for  the  sake  of  tliiH,  but  it  was  the  result  of 
accident.  And  in  like  manner  as  to  the  other  parts  in  which  there  appears  to  exist 
nn  adaptation  to  an  end.  Wheresoever,  therefore,  all  things  together  ^tllat  is,  all  tho 
parts  of  one  whole)  happened  like  as  if  they  were  made  for  the  sake  of  something, 
these  were  preserved,  having  been  appropriately  constituted  by  an  internal  spon- 
taneity ;  and  whatsoever  things  were  not  thus  constituted  perished,  and  still  perish." 
Wo  hero  sec  the  principle  of  natural  selection  shadowed  forth ;  but  how  little 
Aristotle  fully  comprehended  the  principle  is  shown  byhia  remarks  on  the  formation 
of  tho  teeth. 


10  IIISTOKICAL  SKETCH. 

conclusion  on  the  graJiuil  cliangc  of  species  by  the  dilTicully  of  distinguish- 
ing species  and  varieties,  bj-  the  almost  perfect  gradation  of  forms  in  certain 
groups,  and  by  the  analogy  of  domestic  productions.  With  respect  to  the 
means  of  modification,  he  attributed  something  to  the  direct  action  of  the 
physical  conditions  of  life,  something  to  the  crossing  of  already  existing 
forms,  and  much  to  use  and  disuse — that  is,  to  the  efTccts  of  habit.  To  this 
latter  agency  he  seems  to  attribute  all  the  beautiful  adaptations  in  Nature — 
such  as  the  long  neck  of  the  giraffe  for  browsing  on  the  branches  of  trees. 
But  he  likewise  believed  in  a  law  of  progressive  development ;  and,  as  all 
the  forms  of  life  thus  tend  to  progress,  in  order  to  account  for  the  existence 
at  the  present  day  of  simple  productions,  he  maintains  that  such  forms  arc 
now  spontaneously  generated.* 

Geoffroy  Saint-IIilaire,  as  is  stated  in  his  "Life,"  written  by  his  son,  sus- 
pected, as  early  as  IvOo,  that  what  we  call  species  are  various  degenerations 
of  the  same  type.  It  was  not  until  1828  that  he  puljjishcd  his  conviction 
that  the  same  forms  have  not  been  perpetuated  since  the  origin  of  all  things. 
Geoffroy  seems  to  have  relied  chiefly  on  the  conditions  of  life,  or  the  "  monde 
ambiant,''^  as  the  cause  of  change.  lie  was  cautious  in  drawing  conclusions, 
and  did  not  believe  that  existing  species  are  now  undergoing  modification  ; 
and,  as  his  son  adds,  "  C'cst  done  un  probleme  h,  reserver  cntierement  h 
I'avenir,  suppos6  meme  que  I'avenir  doive  avoir  prise  sur  lui." 

In  1813  Dr.  "W.  C.  AVells  read  before  the  Eoyal  Society  "An  Account 
of  a  White  Female,  Part  of  whose  Skin  resembles  that  of  a  Negro;"  but 
his  paper  was  not  published  until  his  famous  "  Two  Essays  upon  Dew  and 
Single  Vision  "  appeared,  in  1818.  In  this  paper  he  distinctly  recognizes 
the  principle  of  natural  selection,  and  this  is  the  first  recognition  which  has 
been  indicated  ;  but  he  applies  it  only  to  the  races  of  man,  and  to  certain 
characters  alone.  After  remarking  that  negroes  and  mulattoes  enjoy  an  im- 
nniuity  from  certain  tropical  di.-cases,  he  observes,  firstly,  that  all  animals 

*  I  have  taken  the  date  of  tlic  first  publication  of  Lamarck  from  Isid.  Qeofl'roy 
Saint-Ililaire'8  ("Hist.  Nat.  Guncralc,"  torn.  11.,  p.  405,  1S50)  cxrcllent  history  of 
opinion  on  this  subject.  In  this  work  a  full  account  is  pivcn  of  Buftbn's  conclusious 
on  the  pame  subject.  It  is  curious  how  largely  my  grandfather,  Dr.  Erasmus  Dar. 
win,  anticipated  the  views  and  erroneous  grounds  of  opinion  of  Lamarck  in  Iiis 
"Zoononiia"  (vol.  i.,  pp.  500-510),  published  in  ITUt.  According  to  Isid.  Geoffroy, 
there  is  no  doubt  that  Goethe  was  an  extreme  partisan  of  similar  views,  ns  shown 
in  llic  introduction  to  a  work  written  in  1794  and  1795,  but  not  published  <\\\  long 
afterward:  he  has  pointedly  remarked  ("Goethe  als  Naturforsclicr,"  von  Dr.  Karl 
Meding,  s.  31)  tbat  the  future  question  for  naturalists  will  be  how,  for  Instance,  cattle 
got  tlielr  horns,  and  not  for  wbat  they  are  used.  It  is  rather  a  singular  instance  of 
the  manner  in  wliieh  similar  views  arise  at  about  the  same  time,  that  Goethe  in  Ger- 
many, Dr.  Darwin  in  England,  and  (icoffroy  Saint-Ililai re  (as  we  shall  immediately 
eee)  in  France,  came  to  the  same  conclusion  on  the  origin  of  species,  in  the  years 
1794-'95. 


niSTOKICAL  SKETCH.  H 

tend  to  varj-  iu  some  deforce,  and,  secondly,  that  agriculturists  improve  their 
domesticated  animals  by  selection ;  and  then,  he  adds,  but  what  is  done  in 
this  latter  case  "  by  art  seems  to  be  done  with  equal  cdicacy,  though  more 
slowly,  by  Nature,  in  the  formation  of  varieties  of  mankind,  fitted  for  the 
country  which  they  inhabit.  Of  the  accidental  varieties  of  man,  which 
would  occur  among  the  first  few  and  scattered  inhabitants  of  the  middle 
regions  of  Africa,  some  one  would  be  better  fitted  than  the  others  to  bear 
the  diseases  of  the  country.  This  race  would  consequently  multiply,  while 
the  others  would  decrease — not  only  from  their  inability  to  sustain  the  at- 
tacks of  disease,  but  from  their  incapacity  of  contending  with  their  more 
vigorous  neighbors.  The  color  of  this  vigorous  race,  I  take  for  granted, 
from  what  has  been  already  said,  would  be  dark.  But,  tlie  same  disposition 
to  form  varieties  still  existing,  a  darker  and  a  darker  race  would  in  the 
course  of  time  occur ;  and,  as  the  darkest  would  be  the  best  fitted  for  the 
climate,  this  would  at  length  become  the  most  prevalent,  if  not  the  only, 
race  in  the  particular  country  in  which  it  had  originated."  lie  then  extends 
these  same  views  to  the  white  inhabitants  of  colder  climates.  I  am  in- 
debted to  Mr.  Rowley,  of  the  Uniteil  States,  for  having  called  my  attention, 
through  Mr.  Brace,  to  the  above  passage  in  Dr.  Wells's  work. 

The  lion,  and  Kcv.  W.  Herbert,  afterward  Dean  of  Manclicster,  in  the 
fourth  volume  of  the  "  Horticultural  Transactions,"  1822,  and  in  his  work  on 
the  "  Amaryllidacere  "  (1S37,  pp.  10,  339),  declares  that  "  horticultural  exper- 
iments have  established,  beyond  the  possibility  of  refutation,  that  botanical 
species  are  only  a  higher  and  more  permanent  class  of  varieties."  He  ex- 
tends the  same  view  to  animals.  The  dean  believes  that  single  species  of 
each  genus  were  created  in  an  originally  highly  plastic  condition,  and  that 
these  have  produced,  chiefly  by  intercrossing,  but  likewise  by  variation,  all 
ovir  existing  species. 

In  182G  Professor  Grant,  in  the  concluding  paragraph  in  his  well-known 
paper  {Edinhtirgh  Philosoplikal  Journal,  vol.  xiv.,  p.  283)  on  the  Spongilla, 
clearly  declares  his  belief  that  species  are  descended  from  other  species,  and 
that  they  become  improved  in  the  course  of  modification.  This  same  view 
was  given  in  his  55th  Lecture,  published  in  the  Lancet  in  1834. 

In  1831  Mr.  Patrick  Matthew  published  his  work  on  "Xaval  Timl)er  and 
Arboriculture,"  in  which  he  gives  precisely  the  same  view  on  the  origin  of 
species  as  that  (presently  to  be  alluded  to)  propounded  by  ^Ir.  Wallace  and 
myself  in  the  Lluncan  Journal,  and  as  that  enlarged  in  the  present  volume. 
Unfortunately,  the  view  was  given  by  Mr.  Matthew  very  briefly  in  scattered 
passages  in  an  Appendix  to  a  work  on  adiflcrcnt  sul)jeet,  so  that  it  remained 
unnoticed  until  Mr.  Matthew  himself  drew  attention  to  it  in  the  Gardcncr^a 
Chronicle,  on  April  Y,  1860.  The  difTcrcnecs  of  Mr.  JIatthew's  view  from 
mine  arc  not  of  much  importance  ;  he  seems  to  consider  that  the  world  was 


12  HISTORICAL  SKETCH. 

nearly  depopulated  at  successive  periods,  and  then  restocked ;  and  he  gives, 
as  an  alternative,  that  new  forms  may  be  generated  "  without  the  presence 
of  any  mould  or  germ  of  former  aggregates."  I  am  not  sure  that  I  under- 
stand some  passages  ;  but  it  seems  tliat  he  attributes  much  influence  to  the 
direct  action  of  the  conditions  of  life.  He  clearly  saw,  however,  the  full 
force  of  tlie  principle  of  natural  selection. 

The" celebrated  geologist  and  naturalist.  Yon  Buch,  in  his  excellent  "De- 
scription Physique  dcs  lies  Canaries"  (1836,  p.  147),  clearly  expresses  his 
belief  that  varieties  slowly  become  changed  into  permanent  species,  which 
arc  no  longer  capable  of  intercrossing. 

Rafinesquc,  in  his  "New  Flora  of  North  America,"  published  in  1836, 
wrote  (p.  C)  as  follows :  "  All  species  might  have  been  varieties  once,  and 
many  varieties  are  gradually  becoming  species  by  assuming  constant  and  pe- 
culiar characters:"  but  further  on  (p.  18)  he  adds,  "except  the  original 
types  or  ancestors  of  the  genus." 

In  1813-41  Prof.  Ilaldcman  {Boston  Journal  of  Nat.  ///.s/.,  U.  States,  vol. 
iv.,  p.  463)  has  ably  given  the  arguments  for  and  against  the  hypothesis  of 
the  development  and  modification  of  species ;  he  seems  to  lean  toward  the 
side  of  change. 

The  "  Ycstigcs  of  Creation"  appeared  in  1844.  In  the  tenth  and  much 
improved  edition  (1853)  the  anonymous  author  says  (p.  155):  "The  propo- 
sition determined  on  after  much  consideration  is,  that  the  several  series  of 
animated  beings,  from  the  simplest  and  oldest  up  to  the  highest  and  most 
recent,  are,  under  the  providence  of  God,  the  results,  first,  of  an  impulse 
which  has  been  imparted  to  the  forms  of  life,  advancing  them,  in  definite 
times,  by  generation,  through  grades  of  organization  terminating  in  the  high- 
est dicotyledons  and  vertebrata,  these  grades  being  few  in  number,  and  gen- 
erally marked  by  intervals  of  organic  character,  which  we  find  to  be  a  prac- 
tical difficulty  in  ascertaining  affinities;  second,  of  another  impulse  connected 
with  the  vital  forces,  tending,  in  the  course  of  generations,  to  modify  organic 
structures  in  accordance  with  external  circumstances,  as  food,  the  nature  of 
the  habitat,  and  the  meteoric  agencies,  these  being  the  '  adaptations '  of  the 
natural  theologian."  The  author  apparently  believes  thr.t  organization  pro- 
gresses by  sudden  leaps,  but  that  the  eflccts  produced  by  the  conditions  of 
life  arc  gradual.  lie  argues  with  much  force  on  general  grounds  that  species 
arc  not  immutable  productions.  But  I  cannot  see  how  the  two  supposed 
"impulses"  account  in  a  scientific  sense  for  the  numerous  and  beautiful  co- 
adaptations  which  wc  sec  throughout  Nature  ;  I  cannot  see  that  we  thus  gain 
any  insight  how,  for  instance,  a  woodpecker  has  become  adapted  to  its  pecu- 
liar habits  of  life.  "  The  work,  from  its  powerful  and  brilliant  style,  though 
di:<playing  in  the  earlier  editions  little  accurate  knowledge  and  a  gi-eat  want 
of  scientific  caution,  immedi.itcly  had  a  very  wide  circulation.     In  my  opiu- 


IIISTOEICiVL  SKETCH.  13 

ion  it  has  done  excellent  service  in  this  country  in  callinj;  attention  to  the 
subject,  in  removing  prejudice,  and  in  thus  preparing  the  ground  lor  the  re- 
ception of  analogous  views. 

In  1816  the  veteran  geologist,  M.  J.  d'Omalius  d'llalioy,  published  in  au 
excellent,  though  short  paper  {Bulletins  dc  PAcad.  Jioy.  JSi-uxcllcs,  torn, 
xiii.,  p.  581),  his  oinuion  tliut  it  is  more  probable  that  new  species  have  been 
produced  by  descent  with  modification,  than  that  they  have  been  separately 
created.     The  author  first  promulgated  this  opinion  in  1831. 

Trof.  Owen,  in  1819  ("Nature  of  Limbs,"  p.  SO),  wrote  as  follows: 
"  The  archetypal  idea  was  mauirested  in  the  flesh  under  divers  such  modifi- 
cations, upon  this  planet,  long  prior  to  the  existence  of  those  animal  species 
that  actually  exemplify  it.  To  what  natural  laws  or  secondary  causes  the  or- 
derly succession  and  progression  of  such  organic  phenomena  may  have  been 
committed,  we,  as  yet,  are  ignorant."  In  his  Address  to  the  British  Asso- 
ciation, in  1858,  he  speaks  (p.  li.)  of  "the  axiom  of  the  continuous  operation 
of  creative  pow'er;  or  of  the  ordained  becoming  of  living  things."  Further  on 
(p.  xc),  after  referring  to  geograpliical  distribution,  he  adds  :  "  These  phe- 
nomena shake  our  confidence  in  the  conclusion  that  the  Apteryx  of  New 
Zealand  and  the  Red  Grouse  of  England  were  distinct  creations,  in  and  for 
tho.^e  islands  respectively.  Always,  also,  it  may  be  well  to  bear  in  mind 
that  by  the  word  'creation'  the  zoologist  means  'a  process  he  knows  not 
what.'  "  lie  amplifies  this  idea  by  adding  that,  when  such  eases  as  that  of 
the  IJed  Grouse  arc  "  enumerated  by  the  zoologist  as  evidence  of  distinct 
creation  of  the  bird  in  and  for  such  islands,  he  chiefly  expresses  that  he 
knows  not  how  the  lied  Grouse  came  to  be  there,  and  there  exclusively,  sig- 
nifying also,  by  this  mode  of  expressing  such  ignorance,  his  belief  that  both 
the  bird  and"  the  islands  owed  their  origin  to  a  great  first  Creative  Cause." 
If  we  interpret  these  sentences  given  in  the  same  Address,  one  by  the  other, 
it  appears  that  this  eminent  philosopher  felt,  in  1858,  his  confidence  shaken 
that  the  Apteryx  and  the  Red  Grouse  first  appeared  in  their  respective 
homes,  "he  knew  not  how,"  or  by  some  process,  "he  knew  not  what." 

This  Address  was  delivered  after  the  papers,  by  Mr.  "Wallace  and  myself, 
on  the  Origin  of  .'Species,  presently  to  be  referred  to,  had  been  read  before 
the  Linnean  Society.  "When  the  first  edition  of  this  work  was  published,  I 
was  so  completely  deceived,  as  were  many  others,  by  such  expressions 
as  "the  continuous  operation  of  creative  power,"  that  I  included  Prof. 
Owen  with  other  paleontologists,  as  being  firmly  convinced  of  the  immuta- 
bility of  species ;  but  it  appears  ("Anat.  of  Vertebrates,"  vol.  iii.,  p.  796)  that 
this  was  on  my  part  a  preposterous  error.  In  the  last  edition  of  this  work  I 
inferred — and  the  inference  still  seems  to  bo  perfectly  just — from  a  passage 
beginning  with  the  words  "  no  doubt  the  type-form,"  etc.  (ibid.,  vol.  i.,  p. 
XXXV.),  that  Prof.    Owen  admitted   that  natural  selection   may  have  done 


1 4  IIISTOKICAL  SKETCH. 

Bometliinp;  in  tlio  foriuation  of  new  ppccics ;  but  tliir:,  it  appears  (ibiil.,  vol. 
ii.,  p.  708),  is  inaccurate  and  witliout  evidence.  I  also  gave  some  extracts 
from  a  correspondence  between  Prof.  Owen  and  the  editor  of  the  Lon- 
don licvicw,  from  which  it  appeared  manifest  to  the  editor  as  well  as  to 
myself,  that  Prof.  Owen  claimed  to  have  promulgated  the  theory  of  nat- 
ural selection  before  I  had  done  so ;  and  I  expressed  my  surprise  and  satis- 
faction at  this  announcement ;  but,  as  far  as  it  is  possible  to  understand  cer- 
tain reccntl}--published  passages  (ibid.,  vol.  iii.,  p.  "JOS),  I  have,  cither  par- 
tially or  wholly,  again  fallen  into  error.  It  is  consolatory  to  me  that  others 
find  Prof.  Owen's  controversial  writings  as  difficult  to  understand,  and 
to  reconcile  with  each  other,  as  I  do.  As  far  as  the  mere  enunciation  of 
the  principle  of  natural  selection  is  concerned,  it  is  quite  immaterial  whether 
or  not  Prof.  Owen  preceded  me,  for  both  of  us,  as  shown  in  tliis  historical 
sketch,  were  long  ago  preceded  by  Dr.  "Wells  and  Mr.  Matthew. 

M.  Isidore  GcoflVoy  Saint-IIilaire,  in  his  Lectures  delivered  in  1850  (of 
which  a  resume  appeared  iu  the  Hevue  ctMn(/.  dc  ZooJog.^  January,  1851), 
briefly  gives  his  reason  for  believing  that  specific  characters  "  sont  fixes, 
pour  chaque  esijuce,  tant  qu'elle  se  perpetue  au  milieu  des  m6mes  circon- 
stanccs:  lis  se  modifient,  si  Icscirconstanccsambiantcs  vienncnti  changer." 
"En  r6sume,  Vohservation  des  animaux  sauvages  dcmontre  dejiHavariabihte 
limiiie  des  cspeces.  Les  experiences  sur  Ics  animaux  sauvages  dcvcnus  do- 
mcstiqucs,  ct  sur  les  animaux  domestiques  redcvenus  sauvages,  la  demon- 
trent  plus  claircment  encore.  Ccs  memcs  experiences  prouvcnt,  deplus,  que 
les  diirercnces  produites  peuvent  ctre  de  valcur  gcniriqne.''^  In  his  "  Hist. 
Nat.  Generalc"  (tom.  ii.,  p.  430,  1859)  he  amplifies  analogous  conclusions. 

From  a  circular  lately  issued  it  appears  that  Dr.  Frekc,  in  1851  {Dublin 
Medical  Frcsa,  p.  322),  propounded  the  doctrine  that  all  organic  beings  have 
descended  from  one  primordial  form.  His  grounds  of  belief  and  treatment 
of  the  subject  are  wholly  diflVrent  from  mine;  but,  as  Dr.  Freke  has  now 
(1801)  ptiblishcd  his  Essay  on  the  "Origin  of  Species  by  means  of  Organic 
Affinity,"  the  difficult  attempt  to  give  any  idea  of  his  views  would  be  super- 
fluous on  my  part. 

Mr.  Herbert  Spencer,  in  an  Essay  (originally  published  in  the  Leader, 
March,  1852,  and  republished  in  his  "  Essays  "  in  1858),  has  contrasted  the 
theories  of  the  Creation  and  the  Development  of  organic  beings  with  re- 
markable skill  and  force.  He  argues  from  the  analogy  of  domestic  pro- 
ductions, from  the  changes  which  the  embryos  of  many  species  undergo, 
from  the  difficulty  of  distinguishing  species  and  A-arictics,  and  from  the  prin- 
ciple of  general  gradation,  that  species  have  been  modified  ;  and  he  attributes 
the  modification  to  the  change  of  circumstances.  The  author  (1855)  has 
also  treated  Psychology  on  the  principle  of  tliencce.-sary  acquirement  of  each 
mental  power  and  capacity  by  gradation. 


HISTORICAL  SKETCH.  15 

In  1852  M.  Naudin,  a  distinguished  botanist,  expressly  stated,  in  an  ad- 
mirable paper  on  the  Origin  of  Species  {Revue  Horlkolc^  p.  102 ;  sir.ce 
partlj'  republished  in  the  "Nouvelles  Archives  du  Museum,"  torn,  i.,  p. 
171),  his  belief  that  species  are  formed  in  an  analogous  manner  as  varie- 
ties arc  under  cultivation ;  and  the  latter  process  he  attributes  to  man's 
power  of  selection.  But  he  does  not  show  how  selection  acts  under  Nature. 
lie  believes,  like  Dean  Herbert,  that  species,  when  nascent,  were  more 
plastic  than  at  present.  lie  lays  weight  on  what  he  calls  the  principle  of 
linality,  "puissance  mysturieusc,  indeterminee;  fatalite  pour  les  uns ;  pour 
les  autres,  volonto  providentielle,  dont  Taction  inecssante  sur  les  etres  vi- 
vants  determine,  ii  toutcs  les  epoqucs  de  Texistcncc  du  mondc,  la  forme,  Ic 
volume,  et  la  durcc  do  chacun  d'cux,  en  raison  dc  sa  destiuC-e  dans  I'ordre 
de  choses  dont  il  fait  partie.  C'est  cette  puissance  qui  harmonise  chaquc 
membrc  i  rensemble  en  I'appropriant  h.  la  fonction  qu'il  doit  rcmplir  dans 
Torganisme  general  de  la  nature,  fonction  qui  est  pour  lui  sa  raison 
d'etre"* 

In  1853  a  celebrated  geologist.  Count  Keyscrling  {BuV.ei'ni  ilc  la  Soc. 
Gcohg.,  2d  Scr.,  tom.  x.,  p.  SSV),  suggested  that  as  new  diseases,  supposed 
to  have  been  caused  by  some  miasma,  have  arisen  and  spread  over  the 
world,  so  at  certain  periods  the  germs  of  existing  species  may  have  been 
cliemically  affected  by  circumambient  molecules  of  a  particular  nature,  and 
thus  have  given  rise  to  new  forms. 

In  this  same  year,  1853,  Dr.  SchaalTliauscn  published  an  excellent  pam- 
phlet ("  Yerhand.  des  Naturhist.  Yereins  dcr  Prcus.-!.  Ilhcinlands,"  etc.),  in 
which  he  maintains  the  progressive  development  of  organic  forms  on  the 
earth.  lie  infers  that  many  species  have  kept  true  for  long  periods, 
whereas  a  few  become  modified.  The  distinction  of  species  he  explains 
by  the  destruction  of  intermediate  graduated  forms.  "  Thus  living  plants 
and  animals  are  not  separated  from  the  extinct  by  new  creations,  but  are  to 
be  regaiilod  as  their  descendants  through  continued  reproduction." 

A  well-known  French  botanist,  51.  Lccoq,  writes  in  185-1  ("Etudes  sur 

♦  From  rofcrcnccs  in  Bronn's  "  Untcrsucluui^xon  iibcr  die  Entwifkchins-'-Oe- 
pptze  "  it  nppca^^^  that  the  celebrated  botanist  and  paleontologifit  Unser  published  in 
]S5'2  his  belief  that  Bpcclcs  undergo  development  and  modillcntion.  D'Alton,  likc- 
wi!»c,  in  Pander  and  Dalton's?  work  on  Fosfil  Slothp,  cxprcc-scd,  in  1821,  a  similar 
belief.  Similar  views  have,  as  is  well  known,  been  uinintained  by  Okcn  in  his  mys- 
tical "  Niitur-PhiloKophic."  From  other  refcrencci?  in  Godron's  work  "Siir  VEi- 
pc^co,"  it  seems  that  Bory  St.  Vinecut,  Burdacli,  Poiret,  and  Fries,  have  all  admitted 
that  new  species  are  continually  bciii:;  produced. 

I  may  add  that,  of  the  thirfy-foiir  authors  named  in  this  lliKtnrical  Skcicli,  who 
believe  In  the  modification  of  species,  or  nt  leasit  disbelieve  in  sepanite  acts  of 
creation,  twenty-seven  have  written  on  special  branches  of  natural  history  or 
geology. 


16  HISTORICAL  SKETCH. 

Geograph.  Bot.,"  torn,  i.,  p.  250),  "  Oa  voit  que  nos  rcchcrchcs  sur  la  fixate 
ou  la  variation  ilc  Tespece,  nous  conduiscnt  dircctcment  aux  idecs  emisea 
par  deux  honiincs  justcmcnt  celebrcs,  Geofifroy  Saint-llilairc  ct  Goethe." 
Some  other  passages,  scattered  through  M.  Lccoq's  large  work,  make  it  a 
little  doubtful  how  far  he  extends  his  views  on  the  modification  of  species. 

The  "  Philosophy  of  Creation  "  has  been  treated  in  a  masterly  manner 
by  the  Rev.  Baden  Powell,  in  his  "Essays  on  the  Unity  of  Worlds,"  1855. 
Nothing  can  be  more  striking  than  the  manner  in  which  he  shows  that  the 
introduction  of  a  new  species  is  "  a  regular,  not  a  casual  phenomenon,"  or, 
as  Sir  John  llerschel  expresses  it,  "  a  natural  in  contradistinction  to  a  mi- 
raculous process." 

The  third  volume  of  the  Journal  of  the  Linnean  Sociehj  contains 
papers,  read  July  1,  1858,  by  Mr.  Wallace  and  myself,  in  which,  as  stated  in 
the  introductory  remarks  to  this  volume,  the  theory  of  Natural  Selection  is 
promulgated  by  Mr.  Wallace  with  admirable  force  and  clearness. 

Yon  Baer,  toward  whom  all  zoologists  feel  so  profound  a  respect,  ex- 
pressed, about  the  year  1859  (see  Prof.  Rudolph  Wagner,  "  Zoologisch-An- 
thropologische  Untcrsuchungen,"  1861,  s.  51),  his  conviction,  chiefly  grounded 
on  the  laws  of  geographical  distribution,  that  forms  now  perfectly  distinct 
have  descended  from  a  single  parent-form. 

In  June,  1859,  Prof.  Huxley  gave  a  lecture  before  the  Royal  Institution 
on  the  "Persistent  Types  of  Animal  Life."  Referring  to  such  cases,  he  re- 
marks :  "  It  is  difficult  to  comprehend  the  meaning  of  such  facts  as  these,  if 
we  suppose  that  each  species  of  animal  and  plant,  or  each  great  type  of  or- 
ganization, was  formed  and  placed  upon  the  surface  of  the  globe  at  long 
intervals  by  a  distinct  act  of  creative  power ;  and  it  is  well  to  recollect  that 
such  an  assumption  is  as  unsupported  by  tradition  or  revelation,  as  it  is  op- 
posed to  the  general  analogy  of  Nature.  If,  on  the  other  hand,  we  view 
'  Persistent  Types'  in  relation  to  that  hypothesis  which  supposes  the  species 
living  at  any  time  to  be  the  result  of  the  gradual  modification  of  pre- 
existing species — a  hypothesis  which,  though  unproven,  and  sadly  damaged 
by  some  of  its  supporters,  is  yet  the  only  one  to  which  physiology  lends  any 
countenance ;  their  existence  would  seem  to  show  that  the  amount  of  modi- 
fication which  living  beings  have  undergone  during  geological  time  is  but 
very  small  in  relation  to  the  whole  scries  of  changes  which  they  have  suf- 
fered." 

In  December,  1859,  Dr.  Hooker  published  his  "  Introduction  to  the  Aus- 
tralian Flora."  In  the  first  part  of  this  great  work  he  admits  the  truth  of 
the  descent  and  modiCcatiou  of  species,  and  supports  this  doctrine  by  many 
original  observations. 

The  first  edition  of  this  work  was  published  on  November  24,  1850,  and 
the  second  edition  on  January  7,  18G0. 


ON    THE    ORIGIN    OF    SPECIES. 


INTRODUCTION. 

When  on  board  H.  M.  S.  "  Beagle,"  as  naturalist,  I  -was 
much  struck  -with  certain  facts  in  the  distribution  of  the  organic 
beings  inhabiting  South  Amdrica,  and  in  the  geological  rela- 
tions of  the  present  to  the  past  inhabitants  of  that  continent. 
These  facts,  as  will  be  seen  in  the  latter  chapters  of  this  volume, 
seemed  to  throw  some  light  on  the  origin  of  species — that 
mystery  of  mysteries,  as  it  has  bcei\  called  by  one  of  our  great- 
est pliiloso^ihcrs.  On  my  return  home,  it  occurred  to  me,  in 
1837,  that  something  might  perhaps  be  made  out  on  this  ques- 
tion by  patiently  accumulating  and  reflecting  on  all  sorts  of 
facts  which  could  possibly  have  any  bearing  on  it.  After  five 
years'  work  I  allowed  myself  to  speculate  on  the  subject,  and 
drew  up  some  short  notes ;  these  I  enlarged  in  1844  into  a 
sketch  of  the  conclusions,  which  then  seemed  to  me  probable : 
fiom  that  period  to  the  present  day  I  have  steachly  pursued 
tlie  same  object.  I  hope  that  I  may  be  excused  from  entering 
on  these  personal  details,  as  I  give  them  to  show  that  I  have 
not  been  hasty  in  coming  to  a  decision. 

My  work  is  now  nearly  finished  ;  but  as  it  will  take  me  two 
or  three  more  years  to  complete  it,  and  as  my  health  is  far 
from  strong,  I  have  been  urged  to  publish  this  Abstract.  I 
have  more  especially  been  induced  to  do  this,  as  Mr.  Wallace, 
who  is  now  studying  the  natural  history  of  the  Malay  archi- 
pelago, has  arrived  at  almost  exactly  the  same  general  conclu- 
sions that  I  have  on  the  origin  of  species.  In  1858  he  sent  me 
a  memoir  on  this  subject,  with  a  request  that  I  would  forward 
it  to  Sir  Charles  Lycll,  who  sent  it  to  the  Linnean  Society,  and 


18  INTRODUCTION. 

it  is  published  in  the  third  vohime  of  the  Journal  of  tliat  So- 
ciety, Sir  C  Lycll  :uid  Dr.  Hooker,  who  both  Icnew  of  my 
work — tlic  hitter  having  read  my  sketch  of  1844 — honored  me 
by  thinking  it  advisable  to  publish,  with  Mr.  Wallace's  excel- 
lent memoir,  some  brief  extracts  from  my  manuscripts. 

This  Abstract,  -which  I  now  publish,  must  necessarily  be 
imperfect.  I  cannot  here  give  references  and  authorities  for 
my  several  statements  ;  and  I  must  trust  to  the  reader  reposing 
some  confidence  in  my  accurac}'.  No  doubt  errors  Avill  have 
crept  in,  tliough  I  hope  I  have  always  been  cautious  in  trust- 
ing to  good  authorities  alone.  I  can  here  give  only  the  general 
conclusions  at  which  I  have  arrived,  with  a  few  facts  in  illustra- 
tion, but  which,  I  hope,  in  most  cases  will  suffice.  No  one  can 
feel  more  sensible  than  I  do  of  the  necessity  of  hereafter  pul> 
lishing  in  detail  all  the  facts,  Avith  references,  on  wliich  my 
conclusions  have  been  grounded ;  and  I  hope  in  a  future  work 
to  do  this.  For  I  am  well  aware  that  scarcely  a  single  point 
is  discussed  in  this  volume  on  Avjiich  facts  cannot  be  adduced, 
often  apparently  leading  to  conclusions  directly  opposite  to 
those  at  Avhich  I  have  arrived.  A  fair  result  can  be  obtained 
only  by  fully  stating  and  balancing  tlie  facts  and  arguments 
on  both  sides  of  each  question ;  and  this  is  here  imj^ossible. 

I  much  regret  that  Avant  of  space  prevents  my  having  the 
satisfaction  of  acknowledging  the  generous  assistance  Avhich  I 
have  received  from  A^ery  many  naturalists,  some  of  them  per- 
sonally unknoAvn  to  me.  I  cannot,  hoAvevcr,  let  this  02')por- 
tunity  pass  Avithout  expressing  my  deep  obligations  to  Dr. 
Hooker,  Avho  for  tlie  last  fifteen  years  has  aided  me  in  CA'ery 
[wssible  Avay  by  his  large  stores  of  knoAAdedge  and  liis  excellent 
judgment. 

In  considering  the  Origin  of  Species,  it  is  quite  conceivable 
that  a  naturalist,  reflecting  on  the  mutual  affinities  of  organic 
beings,  on  their  embryological  relations,  their  geographical 
distribution,  geological  succession,  and  other  such  facts,  might 
come  to  the  conclusion  that  species  had  not  been  independently 
created,  l)ut  had  descended,  like  varieties,  from  other  species. 
Nevertlielcss,  such  a  conclusion,  even  if  Avell  founded,  Avould  be 
unsatisfactory,  imtil  it  could  be  shoAvn  how  the  innumerable 
species  inhabiting  this  Avorld  haA'e  been  modified,  so  as  to  ac- 
quin?  that  perfection  of  structure  and  coadaptation  Avhich  justly 
excites  our  admiration.  Naturalists  continually  refer  to  exter- 
nal conditions,  such  as  climate,  food,  etc.,  as  the  only  possible 
cause  of  variation.     In  one  limited  sense,  as  Ave  shall  hereafter 


INTRODUCTION.  19 

see,  this  may  bo  true  ;  but  it  is  preposterous  to  attribute 
to  mere  exteriuil  conditions,  the  structure,  for  instance,  of 
the  woodpecker,  with  its  feet,  tail,  beak,  and  tonjTue,  so  ad- 
mirably adapted  to  catch  insects  under  the  bark  of  trees.  In 
the  case  of  the  mistletoe,  which  draws  its  nourishment  from 
certain  trees,  M'hich  has  seeds  that  must  be  transported  by  cer- 
tain birds,  and  which  has  flowers  with  separate  sexes  absolutely 
requiring  the  ag^ency  of  certain  insects  to  brin<^  pollen  from  one 
flower  to  the  other,  it  is  equally  preposterous  to  account  for 
the  structure  of  this  parasite,  with  its  relations  to  several  dis- 
tinct organic  beings,  by  the  efl'ects  of  external  conditions,  or 
of  habit,  or  of  the  volition  of  the  plant  itself. 

It  is,  therefore,  of  the  highest  importance  to  gain  a  clear 
insight  into  the  means  of  modification  and  coadaptation.  At 
the  coramencem(mt  of  my  observations  it  seemed  to  me  prob- 
able that  a  carcfyl  study  of  domesticated  animals  and  of  culti- 
vated plants  would  oiler  the  best  chance  of  making  out  this 
obscure  problem.  Nor  have  I  been  disappointed;  in  this  and 
in  all  other  perplexing  cases  I  have  invariably  found  that  our 
knowledge,  imperfect  though  it  be,  of  variation  under  domesti- 
cation, aflbrded  the  best  and  safest  clew.  I  may  venture  to 
express  my  conviction  of  the  high  value  of  such  studies,  al- 
though they  have  been  very  commonly  neglected  by  natural- 
ists. 

From  these  considerations,  I  shall  devote  the  first  chapter 
of  this  Aljstract  to  Variation  under  Domestication.  We  shall 
thus  see  that  a  large  amount  of  hereditary  modification  is  at 
least  possible ;  and,  what  is  equally  or  more  important,  we 
shall  see  how  great  is  the  jiower  of  man  in  accumulating  by 
his  Selection  successive  slight  variations.  I  will  then  pass  on 
to  the  variability  of  species  in  a  state  of  nature ;  but  I  shall, 
unfortunately,  be  compelled  to  treat  this  subject  far  too  briefly, 
as  it  can  be  treated  properly  only  by  giving  long  catalogues 
of  facts.  We  shall,  however,  be  enabled  to  discuss  what  cir- 
cumstances are  most  favorable  to  variation.  In  the  next  chap- 
ter the  Struggle  for  Existence  among  all  organic  beings 
througliout  the  world,  which  inevitably  follows  from  the  high 
geometrical  ratio  of  their  increase,  Avill  be  treated  of.  This  is 
the  doctrine  of  Malthus,  applied  to  the  whole  animal  and  vege- 
table kingdoms.  As  many  more  individuals  of  each  species 
are  born  than  can  possil)ly  survive ;  and  as,  consequently,  there 
is  a  frequently-recurring  struggle  for  existence,  it  follows  that 
any  being,  if  it  vary  however  slightly  in  any  manner  profitable 


20  INTRODUCTION. 

to  itself,  under  tlie  complex  and  sometimes  varying  conditions 
of  life,  uill  have  a  better  chance  of  survivinq-,  and  thus  be  nat- 
la'cdhj  sdectcd.  From  the  strong  principle  of  inheritance,  any 
selected  variety  will  tend  to  propagate  its  new  and  modified 
form. 

This  fundamental  subject  of  Natural  Selection  will  be 
treated  at  some  length  in  tlie  fourth  chapter ;  and  we  shall 
then  see  how  Natural  Selection  almost  inevitably  causes  much 
Extinction  of  the  less  improved  forms  of  life,  and  leads  to  what 
I  have  called  Divergence  of  Character.  In  the  next  chapter  I 
shall  discuss  the  com2:)lcx  and  little-known  laws  of  variation. 
In  the  four  succeeding  chajitcrs,  the  most  apparent  and  gravest 
difficulties  in  accepting  the  theory  will  be  given  :  namely,  first, 
the  difficulties  of  transitions,  or  how  a  simple  being  or  a  simple 
organ  can  be  changed  and  perfected  into  a  highly-developed 
being  or  into  an  elaborately-constructed  organ  ;  secondly,  the 
subject  of  Instinct,  or  the  mental  powers  of  animals ;  thirdly, 
Hybridism,  or  the  infertility  of  species,  and  the  fertility  of  va- 
rieties when  intercrossed ;  and  fourthly,  the  imperfection  of 
the  Geological  Record.  In  the  next  chapter  I  shall  consider 
the  geological  succession  of  organic  beings  throughout  time ; 
in  the  eleventh  and  twelfth,  their  geographical  distribution 
throughout  space  ;  in  the  thirteenth,  their  classification  or  mu- 
tual atlinities,  both  when  mature  and  in  an  embrj-onic  condi- 
tion. In  the  last  chapter  I  shall  give  a  brief  recapitulation  of 
the  whole  work,  and  a  few  concluding  remarks. 

No  one  ought  to  feel  surprise  at  much  remaining  as  yet 
unexplained  in  regard  to  the  origin  of  species  and  varieties,  if 
he  make  due  allowance  for  our  profound  ignorance  in  regard 
to  the  mutual  relations  of  the  many  beings  which  live  around 
us.  AVho  can  explain  why  one  species  ranges  Avidely  and  is 
very  numerous,  and  why  another  allied  species  has  a  narrow 
range  and  is  rare  ?  Yet  these  relations  are  of  the  highest  im- 
]')ortance,  for  they  determine  the  present  welfare,  and,  as  I  be- 
lieve, the  future  success  and  modification  of  every  inhabitant 
of  tins  world.  Still  less  do  we  know  of  tlic  mutual  relations 
of  the  innumerable  inhabitants  of  the  world  during  tlie  man}"- 
past  geological  epochs  in  its  history.  Although  much  remains 
obscure,  and  Avill  long  remain  obscure,  I  can  entertain  no 
doubt,  after  the  most  deliberate  study  and  dispassionate  judg- 
ment of  which  I  am  cajiable,  that  the  view  which  most  natu- 
ralists entertain,  and  which  I  fonnerly  entertained — namely, 
that  each   species  has  been  independently  created — is  erio- 


INTRODUCTION.  21 

neons.  I  am  fully  convinced  that  species  arc  not  immutable , 
but  that  those  belonging  to  what  are  called  the  same  genera 
are  hncal  descendants  of  some  other  and  generally  extinct  spe- 
cies, in  the  same  manner  as  the  acknowledged  varieties  of  any 
one  sjiecies  arc  the  descendants  of  that  species.  Further- 
more, I  am  convinced  that  Natural  Selection  has  been  the 
most  important  but  not  the  exclusive  means  of  modification. 


22  VARIATION  Chap.  I. 


GIIAPTER  I. 

VAEIATION   UNDER   DOMESTICATION. 

C!aii8PS  of  Variability— Effects  of  Habit— Correlated  Variation— Inheritance— Char- 
acter of  Domestic  Varieties — Ditliculty  of  (liHtintruiehinj,'  between  Varieties  and 
Species — Orii^in  of  Dome.stic  Varieties  from  oiie  or  inorc  (species — Domestic 
Pigeons,  their  Differences  and  Origin— Principles  of  Selection,  anciently  followed, 
their  Effects — Methodical  and  Uuconscious  Selection— Unknown  Orisin  of  our 
Domestic  Productions— Circumstances  favorable  to  Man's  Power  of  Selection. 

Causes  of  Yariahility. 

WnEN  we  compare  the  individuals  of  the  same  variety  or 
sub-variety  of  our  older  cultivated  plants  and  animals,  one  of 
the  first  points  which  strikes  us  is,  that  they  generallj'  differ 
from  each  other  more  than  do  the  indi^aduals  of  any  one  spe- 
cies or  variety  in  a  state  of  nature.  And  if  we  reflect  on  the 
vast  diversity  of  the  plants  and  animals  which  have  been  cul- 
tivated, and  which  have  varied  during  all  ages  under  the  most 
different  climates  and  treatment,  Ave  are  driven  to  conclude 
that  this  great  variability  is  due  to  our  domestic  productions 
having  been  raised  under  conditions  of  life  not  so  uniform  as, 
and  somewhat  different  from,  those  to  which  the  parent-species 
had  been  exposed  luider  nature.  There  is  also,  I  think,  some 
probability  in  the  view  propounded  by  Andrew  Knight,  that 
this  variability  may  be  partly  connected  with  excess  of  food. 
It  seems  clear  that  organic  beings  must  be  exposed  during 
several  generations  to  new  conditions  to  cause  any  appreciable 
amount  of  variation  ;  and  that,  when  the  organization  has  once 
l)cgun  to  vary,  it  generally  continues  varying  for  many  gencr- 
atitms.  No  case  is  on  record  of  a  variable  organism  ceasing 
to  vary  imder  cultivation.  Our  oldest  cultivated  plants,  siicli 
as  wheat,  still  yield  new  varieties :  our  oldest  domesticated 
animals  arc  still  capable  of  rapid  improvement  or  modifica- 
tion. 

As  far  as  I  am  able  to  judge,  after  long  attending  to  the 
subject,  the  conditions  of  life  ajipcar  to  act  in  two  ways — di- 


CuAP.  I.  U^'DER  DOMESTICATION.  03 

rcctly  ou  the  -wliole  orn-anizalion  or  on  certain  parts  alone,  and 
indirectly  by  affecting  the  reproductive  system.  With  respect 
to  the  direct  action,  Ave  must  bear  in  mind  that  in  every  case, 
as  Prof.  Weismann  has  lately  insisted,  and  as  I  have  incident- 
ally shown  in  my  -work  on  "  Variation  under  Domestication," 
there  are  two  factors :  namely,  the  nature  of  the  organism,  and 
the  nature  of  the  conditions.  The  former  seems  to  be  much 
the  more  important;  for  nearly  similar  variations  sometimes 
arise  under,  as  far  as  we  can  judge,  dissimilar  conditions ;  and, 
on  the  other  hand,  dissimilar  variations  under  conditions  which 
appear  to  be  nearly  uniform.  The  effects  on  the  offspring  are 
cither  defmite  or  indefmitc.  They  may  be  considered  as  defi- 
nite when  all  or  nearly  all  the  offspring  of  individuals  exposed 
to  certain  conditions  during  several  generations  are  modified 
in  the  same  manner.  It  is  extremely  difficult  to  come  to  any 
conclusion  in  rcgjird  to  the  extent  of  the  changes  which  have 
been  thus  definitely  induced.  There  can,  however,  be  little 
doubt  about  many  slight  changes — such  as  size  from  the 
amoimt  of  food,  color  from  the  nature  of  the  food,  thickness  of 
the  skin  and  hair  from  climate,  etc.  Each  of  the  endless  vari- 
ations which  we  sec  in  the  plumage  of  our  fowls  must  hare 
had  some  efficient  cause ;  and  if  the  same  cause  were  to  act 
uniformly  during  a  long  scries  of  generations  on  many  indi- 
viduals, all  probably  would  be  modified  in  the  same  manner. 
Such  facts  as  the  complex  and  extraordinary  outgrowths 
which  invariably  follow  from  the  insertion  of  a  minute  drop  of 
])oison  by  a  gall-producing  insect,  show  us  what  singular  mod- 
ifications might  result  in  the  case  of  plants  from  a  chemical 
change  in  the  nature  of  the  sap. 

Indefinite  variability  is  a  much  more  common  result  of 
changed  conditions  than  definite  variability,  and  has  probably 
played  a  more  important  part  in  the  formation  of  our  domestic 
races.  We  see  indefinite  Aariability  in  the  endless  slight  pe- 
culiarities which  distinguish  the  individuals  of  the  same  spe- 
cies, and  which  cannot  be  accounted  for  by  inheritance  from 
cither  parent  or  from  some  more  remote  ancestor.  Even 
strongly-marked  differences  occasionally  appear  in  the  young 
of  the  same  litter,  and  in  seedlings  from  the  same  seed-capsules. 
At  long  intervals  of  time,  out  of  millions  of  individuals  rc^ared 
in  the  same  country  and  fed  on  nearly  the  same  fooJ,  dona- 
tions of  structure  so  strongly  pronounced  as  to  deserve  to  be 
called  monstrosities  arise;  but  monstrosities  cannot  be  sepa- 
rated by  any  distinct  Une  from  slighter  variations.     All  such 


24  VARIATION  Chap.  I. 

changes  of  structure,  ■whether  extremely  slight  or  strongly 
marked,  which  appear  among  many  individuals  living  together, 
may  be  considered  as  the  indefinite  elTects  of  the  conditions  of 
life  on  each  individual  organism,  in  nearly  the'  same  manner  as 
a  chill  allxicts  diflerent  men  in  an  indefinite  manner,  according 
to  their  state  of  body  or  constitution,  causing  coughs  or  colds, 
rheumatism,  or  inflammations  of  various  organs. 

With  respect  to  what  I  have  called  the  indirect  action  of 
changed  conditions,  namely,  through  the  reproductive  system 
being  afTected,  Ave  may  infer  that  variability  is  thus  induced, 
partly  from  the  fact  of  this  system  being  extremely  sensitive 
to  any  change  in  the  conditions,  and  partly  from  the  similarity, 
as  Kolreutcr  and  others  have  remarked,  between  the  variabil- 
ity which  follows  from  the  crossing  of  distinct  species,  and 
that  which  may  be  observed  with  all  plants  and  animals 
Avhen  reared  under  new  or  unnatural  conclitions.  Many  facts 
clearly  show  how  eminently  susceptible  the  reproductive  sys- 
tem is  to  very  slight  changes  in  the  surrounding  conditions. 
Nothing  is  more  easy  than  to  tame  an  animal,  and  few  things 
more  difficult  than  to  get  it  to  breed  freely  under  confinement, 
oven  Avhen  the  male  and  female  unite.  How  many  animals 
there  are  Avhich  Avill  not  breed,  though  kept  in  an  almost  free 
state  in  their  native  country  !  This  is  generally,  but  errone- 
ously, attributed  to  vitiated  instincts.  Many  cultivated  plants 
display  the  utmost  vigor,  and  yet  rarely  or  never  seed !  In 
some  few  cases  it  has  been  discovered  that  a  very  trifling 
change,  such  as  a  little  more  or  less  water  at  some  particular 
period  of  growth,  will  determine  whether  or  not  a  plant  will 
produce  seeds.  I  cannot  here  give  the  details  which  I  liave 
collected  and  elscAvhere  published  on  this  curious  subject ;  but, 
to  show  how  singular  the  laws  are  Avhich  determine  the  repro- 
duction of  animals  under  confinement,  I  may  mention  that  car- 
nivorous animals,  even  from  the  tropics,  breed  in  this  country 
pretty  freely  under  confinement,  with  the  exception  of  the 
jilantigrades  or  bear  family,  Avhich  seldom  produce  young; 
whereas  carnivorous  birds,  with  the  rarest  exceptions,  hardly 
ever  lay  fertile  eggs.  Many  exotic  plants  have  jwllen  utterly 
worthless,  in  the  same  condition  as  in  the  most  sterile  hybrids. 
When,  on  the  one  hand,  we  sec  domesticated  animals  and 
jilants,  though  often  weak  and  sickly,  yet  breechng  freely  un- 
der confinement ;  and  when,  on  the  other  hand,  we  see  indi- 
viduals, though  taken  young  from  a  state  of  nature,  ]>erfectly 
tamed,  long-lived,  and  healthy  (of  which  I  could  give  numerous 


Chap.  I.  UNDEIl  DOMESTICATIOin.  25 

instances),  yet  having  their  reproductive  system  so  seriously 
anccted  by  uiiperceived  causes  as  to  fail  to  act,  Ave  need  not 
he  surprised  at  this  system,  when  it  does  act  under  confine- 
UKMit,  acting  irregularly,  and  jiroducing  offspring'  somewhat 
imlike  their  parents.  I  may  adil,  that  as  some  organisms  breed 
fn^ely  under  the  most  unnatural  conditions  (for  instance,  rali- 
bits  and  ferrets  kept  in  hutches),  showing  that  their  reproduc- 
tive organs  arc  not  affected ;  so  will  some  animals  and  plants 
withstand  domestication  or  cultivation,  and  vary  very  slightly 
— perhaps  hardly  more  than  in  a  state  of  nature. 

Some  naturalists  have  maintained  that  all  variations  are 
connected  with  the  act  of  sexual  reproduction ;  but  this  is  cer- 
tainly an  eiTor;  for  I  have  given  in  another  woi'k  a  long  list 
of  "  sporting  plants,"  as  they  are  called  by  gardeners — that  is, 
of  plants  which  have  suddenly  produced  a  single  bud  with  a 
new  and  sometimes  widely-diilerent  character  from  that  of  the 
other  buds  on  the  same  plant.  These  bud-variations,  as  they 
may  be  named,  can  be  propagated  by  grafts,  offsets,  etc.,  and 
sometimes  by  seed.  They  occur  rarely  under  nature,  but  far 
from  rarely  under  culture.  As  a  single  bud  out  of  the  manj^ 
thousands  produced  year  after  year  under  uniform  conditions 
on  the  same  tree,  has  been  known  suddenly  to  assmne  a  new 
character ;  and  as  buds  on  distinct  trees  growing  und(^r  differ- 
ent conditions,  have  sometimes  yielded  nearly  the  same  variety 
— for  instance,  buds  on  peach-trees  producing  nectarines,  and 
buds  on  common  roses  producing  moss-roses — we  clearly  see 
tliat  the  nature  of  the  conditions  is  of  quite  subordinate  impor- 
tance in  comparison  with  the  nature  of  the  organism  in  deter- 
mining each  particular  form  of  variation — of  not  more  impor- 
tance than  the  nature  of  the  spark  by  wliich  a  mass  of  combus- 
t  \h\o  matter  is  ignited,  has  in  determining  the  nature  of  the 
flames. 

Effects  of  Habit ;   Correlated  Variation  /  Inheritance. 

Habits  are  inherited  and  have  a  decided  influence ;  as  in 
the  period  of  the  flowering  of  plants  when  transported  from 
one  climate  to  another.  In  animals  they  have  a  more  marktnl 
effect ;  for  instance,  I  llnd  in  the  domestic  duck  that  the  bones 
of  the  wing  weigh  less  and  the  bones  of  the  leg  more,  in  pro- 
portion to  the  whole  skeleton,  than  do  the  same  bones  in  the 
wild-duck  ;  and  this  change  may  be  safely  attributed  to  the  do- 
mestic duck  flying  mucli  less,  and  walking  more,  than  its  Mild 
]):irents.     The  great  and  inherite<l   development  of  the   udders 


26  VAKIATION  Chap.  I. 

in  cows  and  goats  in  countries  where  they  arc  habitually  milked, 
in  comparison  with  the  state  of  these  organs  in  other  coimtries, 
is  probably  another  instance  of  the  cfl'ects  of  use.  Not  one  of 
our  domestic  animals  can  be  named  which  has  not  in  some 
country  drooping  ears  ;  and  the  view  which  has  been  suggested 
that  the  drooping  is  due  to  the  disuse  of  the  muscles  of  the 
ear,  from  the  animals  being  seldom  alarmed  by  danger,  seems 
probable. 

^lany  laws  regulate  variation,  some  few  of  which  can  be 
dimly  seen,  and  will  hereafter  be  briefly  discussed.  I  will  here 
only  allude  to  what  may  be  called  correlated  variation.  Im- 
portant changes  in  the  embryo  or  larva  will  probably  entail 
changes  in  the  mature  animal.  In  monstrosities,  the  correla- 
tions between  quite  distinct  parts  are  very  curiovis  ;  and  many 
instances  are  given  in  Isidore  Geofl'roy  St.-Hilaire's  great  work 
on  this  subject.  Breeders  believe  that  long  limbs  are  almost 
always  accompanied  by  an  elongated  head.  Some  instances 
of  correlation  are  quite  whimsical :  thus  cats  which  are  entirely 
white  and  have  blue  eyes  are  generally  deaf.  Color  and  coii- 
stitutional  peculiarities  go  together,  of  which  many  remarkable 
cases  could  be  given  among  animals  and  plants.  From  facts 
collected  by  Heusinger,  it  appears  that  white  sheep  and  pigs 
are  injured  by  certain  plants,  while  dark-colored  mdii-iduals  es- 
cape :  Prof.  Wyman  has  recently  communicated  to  me  a  good 
illustration  of  this  fact ;  on  asking  some  farmers  in  Florida  how 
it  was  that  all  their  pigs  were  black,  they  informed  him  that 
the  pigs  ate  the  paint-root  (Lachnanthes),  which  colored  their 
bones  pink,  and  which  caused  the  hoofs  of  all  but  the  black 
varieties  to  drop  off;  and  one  of  the  "crackers"  (i.  e.,  Florida 
squatters)  added,  "we  select  the  black  members  of  a  litter  for 
raising,  as  they  alone  have  a  good  chance  of  living."  Hairless 
dogs  have  imperfect  teeth :  long-haired  and  coarse-haired  ani- 
mals are  apt  to  have,  as  is  asserted,  long  or  many  horns ; 
pigeons  with  feathered  feet  have  skin  between  their  outer 
toes;  pigeons  with  short  beaks  have  small  feet,  and  those 
with  long  beaks  large  feet.  Hence  if  man  goes  on  selecting, 
and  thus  augmenting,  any  peculiarity,  he  will  almost  certainly 
modify  imintentionally  other  parts  of  the  structure,  owing  to 
tlie  mysterigus  laws  of  correlation. 

The  results  of  the  various,  unknown,  or  but  dimly  under- 
stood laws  of  variation  are  infinitely  complex  and  diversified. 
It  is  well  worth  Avhile  can-fiilly  to  study  the  several  treatises 
on  some  of  our  ol<l  cultivated  jilants,  as  on  tlie  ]iyaci:ith,  potato. 


Chap.  I.  UNDER  DOMESTICATION.  27 

even  the  dahlia,  etc. ;  and  it  is  really  surprising  to  note  the 
endless  points  in  structure  and  constitution  in  which  the  varie- 
ties and  sub-varieties  differ  slig'litly  from  each  other.  The 
whole  organization  seems  to  have  become  plastic,  and  tends  to 
depart  in  a  slight  degree  from  that  of  the  parental  type. 

Any  variation  which  is  not  inherited  is  unimportant  for  us. 
But  the  number  and  diversity  of  inheritable  deviations  of  struc- 
ture, both  those  of  slight  and  those  of  considerable  physiological 
importance,  are  endless.  Dr.  Prosper  Lucas's  treatise,  in  two 
large  volumes,  is  the  fullest  and  the  best  on  this  subject.  No 
breeder  doubts  how  strong  is  the  tendency  to  inheritance  :  that 
like  produces  like  is  his  fundamental  belief :  doubts  have  been 
tlirown  on  this  principle  only  by  theoretical  writers.  When 
any  deviation  of  structure  often  appears,  and  we  see  it  in  the 
father  and  child,  we  cannot  tell  Avhether  it  may  not  be  due  to 
the  same  cause  having  acted  on  both  ;  but  when  among  indir 
viduals,  apparently  exposed  to  the  same  conditions,  any  very 
rare  deviation,  due  to  some  extraordinary  combination  of  cir- 
cumstances, appears  in  the  parent — say,  once  among  several 
million  individuals — and  it  reappears  in  the  child,  the  mere 
doctrine  of  chances  almost  compels  us  to  attribute  its  re- 
appearance to  inheritance.  Every  one  must  have  heard  of 
cases  of  albinism,  prickly  sldn,  hairy  bodies,  etc.,  appearing  in 
several  members  of  the  same  family.  If  strange  and  rare  devia- 
tions of  structure  are  really  inherited,  less  strange  and  com- 
moner deviations  may  be  freely  admitted  to  be  inheritable. 
Perhaps  the  correct  way  of  viemng  the  whole  subject,  Avould 
be,  to  look  at  the  inheritance  of  every  character  whatever  as 
tlie  rule,  and  non-inheritance  as  the  anomaly. 

The  hiAvs  governing  inheritance  are  for  tlie  most  part  un- 
Icnown.  No  one  can  say  why  the  same  peculiarity  in  tlifferent 
individuals  of  the  same  species,  or  in  different  species,  is  some- 
tiiucs  inherited  and  sometimes  not  so;  why  the  child  often  re- 
verts in  certain  characters  to  its  grandfather  or  grandmother  or 
more  remote  ancestor ;  why  a  peculiarity  is  often  transmitted 
fi'om  one  sex  to  both  sexes,  or  to  one  sex  alone,  more  commonly 
but  not  exclusively  to  the  like  sex.  It  is  a  fact  of  some  impor- 
tance to  us,  that  jK'culiarities  appearing  in  the  males  of  our 
domestic  breeds  are  ofLen  transmitted,  either  exclusively  or  in 
a  nmch  greater  degree,  to  tlie  males  alone.  A  much  more  im- 
portant rule,  which  I  think  may  be  trusted,  is  that,  at  Avhatevrr 
period  of  life  a  peculiarity  first  appears,  it  tends  to  reappear  in 
the  ollspring  at  a  corresponding  age,  though  sometimes  earlier. 


23  VARIATION  Chap.  I. 

In  many  cases  this  could  not  be  otherwise  :  thus  the  inherited 
pocuharities  in  tlie  horns  of  cattle  could  appear  only  in  the 
oflsprini^  when  nearly  mature  ;  peculiarities  in  the  silkworm 
are  known  to  appear  at  the  corrcsjoondinf^  caterpillar  or  cocoon 
staple.  But  hereditary  diseases  and  some  other  facts  make  mc 
believe  that  the  rule  has  a  Avider  extension,  and  that,  when 
there  is  no  apparent  reason  why  a  peculiarity  should  appear  at 
any  particular  ai^e,  yet  that  it  does  tend  to  appear  in  the  off- 
spring at  the  same  period  at  which  it  first  appeared  in  the  par- 
ent. I  believe  this  rule  to  be  of  the  hig-hest  importance  in 
explaining-  the  laws  of  embryology.  These  remarks  are  of 
course  confined  to  the  first  appearance  of  the  peculiarity,  and 
not  to  its  primary  cause,  which  may  have  acted  on  the  ovules 
or  on  the  male  element ;  in  nearly  the  same  manner  as  in  the 
ofi'spring-  from  a  short-horned  cow  by  a  long-horned  bull,  the 
greater  length  of  horn,  though  appearing  late  in  life,  is  clearly 
due  to  the  male  element. 

Having  alluded  to  the  sul)ject  of  reversion,  I  may  here  refer 
to  a  statement  often  made  by  naturalists — namely,  that  our 
domestic  varieties,  "when  rim  Avild,  gradually  but  invariably  re- 
vert in  character  to  their  aboriginal  stocks.  Hence  it  has  been 
argued  that  no  deductions  can  be  drawn  from  domestic  races 
to  species  in  a  state  of  nature.  I  have  in  vain  endeavored  to 
discover  on  what  decisive  facts  the  above  statement  has  so 
often  and  so  boldly  been  made.  There  Avould  be  great  difli- 
cidiy  in  proving  its  truth  :  we  may  safely  conclude  that  very 
many  of  the  most  strongly-marked  domestic  varieties  could  not 
possibly  live  in  a  wild  state.  In  many  cases  we  do  not  know 
Avhat  the  aboriginal  stock  was,  and  so  could  not  tell  whether 
or  not  nearly  perfect  reversion  had  ensued.  It  Avould  be  ne- 
cessary, in  order  to  prevent  the  effects  of  intercrossing",  that 
only  a  single  variety  should  have  been  turned  loose  in  its  new 
home.  Nevertheless,  as  our  varieties  certainly  do  occasionally 
i-evert  in  some  of  their  characters  to  ancestral  forms,  it  seems 
to  mc  not  improbable,  that,  if  we  could  succeed  in  naturalizing, 
or  were  to  cultivate,  duringmany  generations,  the  several  races, 
for  instance,  of  the  cabbage,  in  very  poor  soil  (in  which  case, 
however,  some  effect  would  have  to  1)C  attributed  to  the  definite 
action  of  the  poor  soil),  they  would  to  a  large  extent,  or 
even  wholly,  revert  to  the  wild  aboriginal  stock.  Whether  or 
not  the  experiment  would  succeed,  is  not  of  great  imjiortance 
for  our  line  of  argument  ;  for  by  the  experiment  itself  the  con- 
ditions of  life  are  chanixed.     If  it  couUl  be  sliown  that  our  do 


CuAr.  I.  UNDER  DOMESTICATION.  29 

incstic  varieties  manifested  a  strong  tendency  to  reversion — • 
that  is,  to  lose  their  acquired  characters,  while  kept  under  the 
same  conditions,  and  while  kept  in  a  considerable  body,  so  that 
free  intercrossin2^  mig-ht  check,  by  blending  together,  any  slight 
deviations  in  their  structure,  in  such  case,  I  grant  that  we  could 
deduce  nothing  from  domestic  varieties  in  regard  to  species. 
But  there  is  not  a  shadow  of  evidence  in  favor  of  this  view :  to 
assert  that  we  could  not  breed  our  cart  and  race  horses,  long 
and  short  horned  cattle,  and  poultry  of  various  breeds,  and 
esculent  vegetables,  for  an  unlimited  number  of  generations, 
would  be  opposed  to  all  experience. 

Character  of  Domestic  Varieties  ;  Difficult}/  of  distinguish- 
inff  heticeen  Varieties  and  Species  y  Origin  of  Domestic 
Varieties  from  one  or  more  /Sjjecies. 

When  we  look  to  the  hereditary  varieties  or  races  of  our 
domestic  animals  and  plants,  and  compare  them  with  closely- 
alUed  species,  wc  generally  perceive  in  each  domestic  race,  as 
already  remarked,  less  uniformity  of  character  than  in  true 
species.  Domestic  races  often  have  a  somewhat  monstrous 
character ;  by  which  I  mean  that,  although  differing  from  each 
other,  and  from  f)thcr  species  of  the  same  genus,  in  several 
trifling  res]iects,  they  often  differ  in  an  extreme  degree  in  some 
one  part,  both  when  compared  one  with  another,  and  more 
especially  when  compared  with  the  species  under  nature  to 
which  they  are  nearest  allied.  With  these  exceptions  (and 
witli  that  of  the  perfect  fertility  of  varieties  when  crossed — a 
subject  hereafter  to  be  discussed),  domestic  races  of  the  same 
species  differ  from  each  other,  only  in  most  cases  in  a  less  de- 
gree, in  the  same  manner  as  do  closely-allied  species  of  the 
same  genus  in  a  state  of  natiu-e.  This  must  be  admitted  as 
true,  for  the  domestic  races  of  many  animals  and  plants  have 
•been  rank(!d  by  some  competent  judges  as  the  descendants  of 
aboriginally  distinct  species,  and  by  other  competent  judges  as 
mere  varieties.  If  any  well-marked  distinction  existed  be- 
tween a  domestic  race  and  a  species,  this  source  of  doubt 
would  not  so  perpetually  recur.  It  has  often  been  stated  that 
domestic  races  do  not  diffcT  from  each  other  in  characters  of 
generic  value.  It  can  ])e  shown  that  this  statement  is  not  cor- 
rect;  but  naturalists  differ  nuich  in  determining  what  char- 
acters are  of  gimerio  value  ;  all  such  valuations  being  at 
present  empirical.  When  it  is  explained  how  genera  origi- 
nate under  nature,  it  will  bo  seen  that  we  have  no  right  to 


so  CIIAEACTEK  OF  Ciiap.  1. 

expect  often  to  find  a  generic  amount  of  difference  in  our  do- 
mesticated races. 

In  attempting  to  estimate  tlie  amount  of  structural  difler- 
encc  between  the  domestic  races  of  the  same  species,  we  are 
soon  involved  in  doubt,  from  not  knowing  whether  they  have 
descended  from  one  or  several  parent-species.  This  point,  if 
it  could  be  cleared  up,  would  be  interesting ;  if,  for  instance, 
it  could  be  shown  that  the  grevhound,  bloodhound,  terrier, 
spaniel,  and  bull-dog,  which  we  all  know  propagate  their  kind 
so  truly,  were  the  offspring  of  any  single  species,  then  such 
facts  would  have  great  weight  in  making  us  doubt  about  the 
immutability  of  the  many  very  closely-allied  natural  species — 
for  instance,  of  the  many  foxes — inhabiting  different  quarters 
of  the  Avorld.  I  do  not  believe,  as  we  shall  presently  see,  that 
the  whole  amount  of  difference  between  the  several  breeds  of 
the  dog  has  been  produced  under  domestication ;  I  believe 
that  some  small  part  of  the  difference  is  due  to  their  having 
descended  from  distinct  species.  In  the  case  of  strongly- 
marked  races  in  some  other  domesticated  species,  there  is 
presumptive,  or  even  strong,  evidence  that  all  are  descended 
from  a  single  wild  stock. 

It  has  often  been  assumed  that  man  has  chosen  for  domes- 
tication animals  and  plants  having  an  extraordinary  inherent 
tendency  to  var}^,  and  likewise  to  withstand  diverse  climates. 
I  do  not  dispute  that  these  capacities  have  added  largely  to 
the  value  of  most  of  our  domesticated  productions ;  but  how 
could  a  savage  possibly  know,  when  he  first  tamed  an  animal, 
M'hether  it  would  vary  in  succeeding  generations,  and  whether 
it  would  endure  other  climates  ?  Has  the  little  variability  of 
the  ass  and  goose,  or  the  small  power  of  endurance  of  warmth 
by  the  reindeer,  or  of  cold  by  the  common  camel,  prevented 
their  domestication  ?  I  cannot  doubt  that  if  other  animals  and 
plants,  equal  in  number  to  our  domesticated  productions,  and 
belonging  to  equally  diverse  classes  and  countries,  were  taken 
from  a  state  of  nature,  and  could  be  made  to  breed  for  an  equal 
number  of  generations  under  domestication,  they  would  on  an 
average  vary  as  largely  as  the  parent-species  of  our  existing 
domesticated  productions  have  varied. 

In  the  case  of  most  of  our  anciently-domesticated  animals 
and  jilants,  it  is  not  possible  to  come  to  any  definite  conclusion, 
whether  they  are  descended  from  one  or  several  wild  species. 
The  argiunent  mainly  relied  on  by  those  who  believe  in  the 
multiple  origin  of  our  domestic  animals  is,  that  we  find  in  the 


Chap.  I.  DOMESTIC  VARIETIES.  31 

most  ancient  times,  on  tlie  monuments  of  Egypt,  and  in  tlie 
lake-habitations  of  Switzerland,  much  diversity  in  the  breeds  ; 
and  that  some  of  these  ancient  breeds  closely  resemble  or  are 
even  identical  with  those  still  existing-.  But  this  only  throws 
far  backward  the  history  of  civilization,  and  shows  that  ani- 
mals Avere  domesticated  at  a  much  earlier  period  than  has  hith- 
erto l>een  supposed.  The  lake-inhabitants  of  Switzerland  cul- 
tivated several  kinds  of  wheat  and  barley,  the  pea,  the  poppy 
t\)v  oil,  and  llax  ;  and  they  possessed  several  domesticatcnl  ani- 
mals ;  they  had  also  commerce  with  other  nations.  All  this 
clearly  shows,  as  Heer  has  remarked,  that  they  had  at  this 
early  ag-c  progressed  considerably  in  civilization ;  and  this 
again  implies  a  long-continued  previous  period  of  less  advanced 
civilization,  during  which  the  domesticated  animals,  kept  by 
the  different  tribes  in  different  districts,  might  have  varied  and 
given  rise  to  distinct  races.  Since  the  discovery  of  flint  tools 
or  celts  in  the  superficial  formations  in  many  parts  of  the  world, 
all  geologists  believe  that  barbax-ian  man  existed  at  an  enor- 
mously remote  period  ;  and  we  know  that  at  the  present  day 
there  is  hardly  a  tribe  so  barbarous  as  not  to  have  domesti- 
cated at  least  the  dog. 

The  origin  of  most  of  our  domestic  animals  will  probably 
forever  remain  vague.  But  I  may  here  state  that,  looking 
to  the  domestic  dogs  of  the  Avholc  world,  I  have,  after  a  la- 
borious collection  of  all  known  facts,  come  to  the  conclusion 
that  several  wild  species  of  Canidre  have  been  tamed,  and  that 
their  blood,  in  some  cases  mingled  together,  llows  in  the  A-eins 
of  our  domestic  breeds.  In  regard  to  sheep  and  goats,  I  can 
form  no  decided  opinion.  From  facts  communicated  to  me  by 
Mr.  Blyth,  on  the  habits,  voice,  constitution,  and  structure  of 
the  humped  Indian  cattle,  it  is  almost  certain  that  they  are  de- 
scended from  a  different  aboriginal  stock  from  our  European 
cattle ;  and  some  competent  judges  believe  that  these  latter 
have  had  two  or  three  wild  progenitors — whether  or  not  those 
deserve  to  be  called  species  or  races.  This  conclusion,  as  Avell 
as  the  specific  distinction  between  the  humped  and  common 
cattle,  may,  indeed,  be  looked  at  as  established  by  the  recent 
admirable  researches  of  Prof.  Kutimeyer.  With  respect  to 
horses,  from  reasons  which  I  cannot  here  give,  I  am  doubtfully 
inclined  to  believe,  in  opposition  to  several  authors,  that  all  the 
races  belong  to  the  saine  species.  Having  kept  nearly  all  the 
English  breeds  of  the  fowl  alive,  having  bred  and  crossed  them, 
and  examined  their  skeletons,  it  appears  to  me  almost  certain 


32  CU^AKACTER  OF  Chap.*. 

that  all  are  the  descendants  of  the  wild  Indian  fowl,  Gallus 
bankiva;  and  Ihis  is  tlie  conclusion  of  Mr.  Bljth,  and  of  others 
who  have  studied  this  bird  in  India.  In  reg'ard  to  ducks  and 
rabbits,  some  breeds  of  which  difler  much  from  each  otiier,  the 
evidence  is  clear  that  they  arc  all  descended  from  the  common 
wild  duck  and  rabbit. 

The  doctrine  of  the  origin  of  our  several  domestic  races  from 
several  aborig'inal  stocks,  has  been  carried  to  an  absurd  ex- 
treme by  some  authors.  They  believe  that  every  race  which 
breeds  true,  let  the  distinctive  characters  be  ever  so  slight, 
has  had  its  wild  protot^qDe.  At  this  rate,  there  must  have  ex- 
isted at  least  a  score  of  species  of  wild  cattle,  as  many  sheep, 
and  several  goats,  in  Europe  alone,  and  several  even  within 
Great  Britain.  One  author  believes  that  there  formerly  existed 
in  Great  Britain  eleven  wild  species  of  sheej?  peculiar  to  it ! 
When  v,e  bear  in  mind  that  Britain  has  now  hardly  one  pecu- 
liar mammal,  and  France  but  few  distinct  from  those  of  Ger- 
many, and  conversely,  and  so  with  Hungary,  Spain,  etc.,  but 
that  each  of  these  kingdoms  possesses  several  peculiar  breeds 
of  cattle,  sheep,  etc.,  we  must  admit  that  many  domestic  breeds 
have  originated  in  Europe  ;  for  whence  have  they  been  derived, 
as  these  several  countries  could  not  possess  so  large  a  number 
of  peculiar  species  for  parent-stocks  ?  So  it  is  in  India.  Even 
in  the  case  of  the  domestic  dogs  of  the  whole  world,  which  I 
admit  to  have  descended  from  several  wild  species,  it  cannot  be 
doubted  that  there  has  been  an  immense  amount  of  inherited 
variation  ;  for  who  will  believe  tliat  animals  closely  resembling 
the  Italian  greyhound,  the  bloodhound,  the  bull-dog,  pug-dog, 
or  Blenheim  spaniel,  etc. — so  xmlike  all  Avild  Canida? — ever  ex- 
isted freely  in  a  state  of  nature  ?  It  has  often  been  loosely 
said  that  all  our  races  of  dogs  have  been  produced  by  the 
crossing  of  a  few  aboriginal  species  ;  but  by  crossing  Ave  can 
only  get  forms  in  some  degree  intermediate  between  their  par- 
ents ;  and  if  we  account  for  our  several  domestic  races  by  this 
process,  we  must  admit  the  former  existence  of  the  most  ex- 
treme forms,  as  the  Italian  greyhound,  bloodhound,  bull-dog, 
etc.,  in  the  wild  state.  Moreover,  the  possibility  of  making 
distinct  races  by  crossing  has  been  greatly  exaggerated.  Many 
cases  are  on  record,  showing  that  a  race  may  be  modified  by 
occasional  crosses,  if  aided  by  the  careful  selection  of  the  in- 
dividuals which  present  the  desired  character;  but  to  obtaui  a 
race  nearly  intermediate  between  two  extronely  dilTerent  races 
or  species,  would  be  very  dillicult.     Sir  J.  Sebright  expressly 


CnAP.  I.  DOMESTIC  VARIETIES.  33 

experimented  for  this  object,  and  failed.  The  oflspriii^v  from 
the  first  cross  between  two  pure  breeds  is  tolerably  and  some- 
times (as  I  have  found  with  pip^eons)  extremely  uniform,  and 
every  thing  seems  simple  enouji-h  ;  but  when  these  mongrels 
are  crossed  one  "with  another  for  several  generations,  hardly 
two  of  them  are  alike  ;  and  then  the  extreme  dilEculty  of  the 
task  becomes  apparent.  Certainly,  a  breed  intermediate  be- 
tween tico  very  distinct  breeds  could  not  be  got  without  ex- 
treme care  and  long-continued  selection  ;  nor  can  I  find  a  case 
on  record  of  a  permanent  race  having  been  thus  formed. 

Breeds  of  the  Domestic  Pigeon,  their  Differences  and  Origin. 

Belie\ing  that  it  is  alwa^'S  best  to  study  some  special  group, 
I  have,  after  deliberation,  taken  up  domestic  pigeons.  I  have 
kept  every  breed  whieli  I  could  purchase  or  obtain,  and  have 
lieen  most  kindly  fav(^red  with  skins  from  several  quarters  of 
the  world,  more  especially  by  the  Hon.  W.  Elliot  from  India, 
and  by  the  Hon.  C.  Murray  from  Persia.  Many  treatises  in 
different  languages  have  been  published  on  pigeons,  and  some 
of  them  are  very  important,  as  being  of  considerable  antiquity. 
I  have  associated  witli  several  eminent  fanciers,  and  have  been 
permitted  to  join  two  of  the  London  Pigeon  Clubs.  The  diver- 
sity of  the  breeds  is  something  astonishing.  Compare  the  Eng- 
lish carrier  and  the  short-faced  tumbler,  and  see  the  Avonderful 
difference  in  tlieir  beaks,  entailing  corresponding  differences  in 
tlieir  skulls.  The  carrier,  more  especially  the  male  bird,  is  also 
remarlvable  from  the  wonderful  development  of  the  caruncu- 
lated  skin  about  the  head;  and  this  is  accompanied  by  greatly- 
elongated  eyelids,  very  large  external  orifices  to  the  nostrils, 
and  a  wide  gape  of  mouth.  The  short-faced  tumbler  has  a 
b(>ak  in  outline  almost  like  that  of  a  finch;  and  the  common 
tuin])ler  has  the  singular  inherited  habit  of  flying  at  a  great 
height  in  a  compact  flock,  and  tumbling  in  the  air  head  over 
heels.  The  runt  is  a  bird  of  great  size,  with  long,  massive  beak 
and  large  feet ;  some  of  tlie  sub-ljreeds  of  runts  have  very  long 
necks,  others  very  long  Avings  and  tails,  others  singularly  short 
tails.  The  barb  is  allied  to  the  carrier,  but,  instead  of  a  long 
beak,  has  a  very  short  and  broad  one.  The  ])outer  has  a  much- 
elongated  body,  wings,  and  legs ;  and  its  enormously  devel- 
oped crop,  which  it  glories  in  inllating,  may  well  excite  aston- 
ishment and  even  laughter.  The  turbit  has  a  very  short  and 
conical  beak,  with  a  line  of  reversed  feathers  down  the  breast; 


34  DOMESTIC  PIGEONS.  Chap.  I. 

and  it  has  the  hal)it  of  continually  expanding  slightly  the  up- 
per part  of  tlie  a?so2:)hagus.  The  Jacobin  has  the  feathers  so 
much  reversed  along  the  back  of  the  neck  that  the}'  form  a 
hood ;  and  it  has,  proportionally  to  its  size,  much-elongated 
wing  and  tail  feathers.  The  trumpeter  and  laugher,  as  their 
names  express,  utter  a  very  different  coo  from  the  otlier  breeds. 
The  fantail  has  thirty  or  even  forty  tail-feathers,  instead  of 
twelve  or  fourteen — the  normal  number  in  all  members  of  the 
great  pigeon  family ;  and  these  feathers  are  kept  expanded, 
and  are  carried  so  erect,  that  in  good  birds  the  head  and  tail 
touch  :  the  oil-gland  is  quite  aborted.  Several  other  less  dis- 
tinct breeds  might  be  specified. 

In  the  skeletons  of  the  several  breeds,  the  development  of 
the  bones  of  the  face  in  length  and  breadth  and  curvature  dif- 
fers enormously.  The  shape,  as  Avell  as  the  breadth  and  length 
of  the  ramus  of  the  lower  jaw,  varies  in  a  highly-remarkable 
manner.  The  caudal  and  sacral  vertebra?  vary  in  number  ;  as 
does  the  number  of  the  ribs,  together  with  their  relative  breadth 
and  the  presence  of  processes.  The  size  and  shape  of  the 
apertures  in  the  sternum  are  highly  variable ;  so  is  the  degree 
of  divergence  and  relative  size  of  the  two  arms  of  the  furcula. 
The  proportional  width  of  the  gape  of  mouth,  the  proportional 
length  of  the  eyelids,  of  the  orifice  of  the  nostrils,  of  the  tongue 
(not  always  in  strict  correlation  with  the  length  of  beak),  the 
size  of  the  crop  and  of  the  upper  part  of  the  ccso})liagus ;  the 
development  and  abortion  of  the  oil-gland ;  the  number  of  the 
primary  wing  and  caudal  feathers  ;  the  relative  length  of  wing 
and  tail  to  each  other  and  to  the  body  ;  the  relative  length  of  leg 
and  of  the  feet ;  the  number  of  scutcHa^  on  the  toes,  the  develop- 
ment of  skin  between  the  toes,  arc  all  points  of  structure  -which 
are  variable.  The  period  at  which  the  perfect  plumage  is  ac- 
quired, varies,  as  does  the  state  of  the  do^^^l  with  which  the  nest- 
ling birds  are  clothed  when  hatched.  The  shape  and  size  of  the 
eggs  vary.  The  manner  of  flight,  and  in  some  breeds  the  voice 
and  disposition,  differ  remarkably.  Lastly,  in  certain  breeds,  the 
males  and  females  have  come  to  dilVer  in  a  slight  degree  from 
each  other. 

Altogether,  at  least  a  score  of  pigeons  might  be  chosen, 
which,  if  shown  to  an  ornithologist,  and  he  were  told  that  they 
were  wild  birds,  would  certainly  be  ranked  by  him  as  well-de- 
fined species.  Moreover,  I  do  not  believe  that  any  ornitliolo- 
gist  would  place  the  English  canicr,  the  short-faced  tumbler, 
the   runt,  tlic  barb,  pouter    and  fantail  in  the  same  genus; 


Chat.  I.  DOMESTIC  TIGEONS.  ,35 

more  especially  as  in  each  of  these  breeds  several  truly-inher- 
ited sub-breeds,  or  s2Dccies  as  he  would  have  called  them,  could 
be  shown  him. 

Great  as  the  differences  are  between  the  breeds  of  pigeons, 
I  am  fully  convinced  that  the  common  opinion  of  naturalists 
is  correct,  namely,  that  all  are  descended  from  the  rock-pigeon 
(Columba  livia),  including  under  this  term  several  geograplii- 
cal  races  or  sul>specics,  Avhich  differ  from  each  other  in  the 
most  trifling  respects.  As  several  of  the  reasons  which  have 
led  me  to  this  belief  are  in  some  degree  applicable  in  other 
cases,  I  will  here  Ijricfly  give  them.  If  the  several  breeds  are 
not  varieties,  and  have  not  proceeded  from  the  rock-pigeon, 
they  must  have  descended  from  at  least  seven  or  eight  abori- 
ginal stocks ;  for  it  is  impossible  to  make  the  present  domestic 
breeds  by  the  crossing  of  any  lesser  number :  how,  for  instance, 
could  a  pouter  be  produced  by  crossing  two  breeds  unless  one 
of  the  parent-stocks  possessed  the  characteristic  enonnous 
crop?  The  supposed  aboriginal  stocks  must  all  have  been 
rock-pigeons,  that  is,  not  breeding  or  willingly  perching  on 
trees.  But  besides  Columba  livia,  Avith  its  geographical  sub- 
species, only  two  or  three  other  species  of  rock-pigeons  are 
known ;  and  these  have  not  any  of  the  characters  of  the 
domestic  breeds.  Hence  the  supposed  aboriginal  stocks  must 
either  still  exist  in  the  countries  where  they  were  originally 
domesticated,  and  yet  be  unknown  to  ornithologists ;  and  this, 
considering  their  size,  habits,  and  remarkable  characters,  seems 
improbable ;  or  they  must  have  become  extinct  in  the  wild 
state.  But  birds  breeding  on  precijiices,  and  good  fliers,  are 
unlikely  to  be  exterminated ;  and  the  common  rock-pigeon, 
which  has  the  same  habits  with  the  domestic  breeds,  has  not 
been  exterminated  even  on  several  of  the  smaller  British  isiecs, 
or  on  the  shores  of  the  Mediterranean.  Hence  the  supposed 
extermination  of  so  many  species  having  similar  habits  with 
the  rock-pigeon  seems  a  very  rash  assumption.  Moreover, 
the  several  above-named  domesticated  breeds  have  been  trans- 
ported to  all  parts  of  tlie  world,  and,  therefore,  some  of  them 
must  have  been  carried  back  again  into  their  native  country; 
but  not  one  has  ever  become  wild  or  feral,  though  the  dovecot- 
pigeon,  which  is  the  rock-pigeon  in  a  very  slightly  altered 
state,  has  become  feral  in  several  places.  Again,  all  recent 
experience  shows  that  it  is  difficult  to  get  any  wild  animal  to 
breed  freely  imder  domestication :  yet,  on  the  hypothesis  of  tlie 
multiple  oritrin  of  our  pigeons,  it  must  be  assumed  that  at  least 


36  ^  DOMESTIC  PIGEONS.  Chap.  I. 

seven  or  eight  species  were  so  thoroughly  domesticated  in 
ancient  times  by  half-civilized  man,  as  to  be  quite  prolific  un- 
der confinement. 

An  argument  of  grcat_  weight,  and  applicable  in  several 
other  cases,  is,  that  the  above-specified  breeds,  though  agree- 
ing generally  with  the  wild  rock-pigeon  in  constitution,  habits, 
voice,  coloring,  and  in  most  parts  of  their  structure,  yet  are 
certainly  highly  abnormal  in  other  parts ;  we  may  look  in  vain 
throughout  the  whole  great  family  of  Columbida?  for  a  beak 
liUe  that  of  the  English  carrier,  or  that  of  the  short-faced  tum- 
bler, or  barb;  for  reversed  feathers  like  those  of  the  Jacobin; 
for  a  crop  like  that  of  the  pouter;  for  tail-feathers  like  those 
of  the  fantail.  Hence  it  must  be  assumed,  not  only  that  half- 
civilized  man  succeeded  in  thoroughly  domesticating  several 
species,  but  that  he  intentionally  or  by  chance  picked  out  ex- 
traordinarily abnormal  species ;  and  further,  that  these  very 
species  have  since  all  become  extinct  or  unknown.  So  many 
strange  contingencies  are  improbable  in  the  highest  degree. 

Some  facts  in  regard  to  the  coloring  of  pigeons  Avell  de- 
serve consideration.  The  rock-pigeon  is  of  a  slaty-blue,  with 
white  loins ;  the  Indian  sub-species,  C  intermedia  of  Strick- 
land, having  this  part  bluish ;  the  tail  has  a  terminal  dark  bar, 
with  the  outer  feathers  externally  edged  at  the  base  with 
white ;  the  wings  have  two  black  bars.  Some  semi-domestic 
breeds,  and  some  truly  wild  breeds,  have,"  besides  the  two 
black  bars,  the  wings  checkered  with  black.  These  several 
marks  do  not  occur  together  in  any  other  species  of  the  Avhole 
family.  Now,  in  every  one  of  the  domestic  breeds,  taking 
thoroughly  well-bred  birds,  all  the  above  marks,  even  to  the 
white  edging  of  the  outer  tail-feathers,  sometimes  concur  per- 
fectly developed.  Moreover,  when  birds  belonging  to  two  or 
more  distinct  breeds  are  crossed,  none  of  Avhich  are  blue  or 
have  any  of  the  above-specified  marks,  the  mongrel  offspring 
are  very  apt  suddenly  to  acquire  these  characters.  To  give 
one  instance  out  of  several  which  I  have  observed :  I  crossed 
some  white  fantails,  which  breed  very  true,  with  some  black 
barbs — and  it  so  happens  that  blue  varieties  of  barbs  are  so 
rare  that  I  never  heard  of  an  instance  in  England;  and  the 
mongrels  were  black,  brown,  and  mottled.  I  also  crossed  a 
barb  with  a  spot,  which  is  a  white  bird  with  a  red  tail  and 
red  spot  on  the  forehead,  and  Avhich  notoriously  breeds  very 
true ;  the  mongrels  were  dusky  and  mottled.  I  then  crossed 
one  of  the  mongrel  barb-fanlails  with  a  mongrel  barb-spot,  and 


Chap.  I.  DOMESTIC   PIGEONS.  37 

tlicy  produced  a  bird  of  as  beautiful  a  bhie  color,  with  the 
white  loius,  double  black  Aviiif^-bar,  and  barred  and  Avliite- 
ed^cd  tail-feathers,  as  any  wild  rock-pi2;'eon  !  We  can  under- 
stand these  facts,  on  the  well-known  principle  of  reversion  to 
ancestral  characters,  if  all  the  domestic  breeds  are  descended 
from  the  rock-])igeoii.  ]}ut  if  we  deny  this,  we  must  make 
one  of  the  two  following;  highly  improbable  suppositions : 
cither,  first,  that  all  the  several  imagined  aboriginal  stocks 
were  colored  and  marked  like  the  rock-pigeon,  although  no 
other  existing  species  is  thus  colored  and  marked,  so  that  in 
each  separate  breed  there  might  be  a  tendency  to  revert  to 
the  very  same  colors  and  markings ;  or,  secondly,  that  each 
breed,  even  the  purest,  has  within  a  dozen,  or  at  most  with- 
in a  score,  of  generations,  been  crossed  by  the  rock-pigeon : 
I  say  within  a  dozen  or  twenty  generations,  for  no  instance 
is  known  of  crossed  descendants  reverting  to  an  ancestor 
of  foreign'  blood,  removed  by  a  greater  nmnbcr  of  genera- 
tions. In  a  breed  which  has  been  crossed  only  once,  the 
tendency  to  revert  to  any  character  derived  from  such  a  cross 
will  naturall}'^  become  less  and  less,  as  in  each  succeeding 
generation  there  will  be  less  of  the  foreign  blood ;  but  when 
there  has  been  no  cross,  and  there  is  a  tendency  in  the  breed 
to  revert  to  a  character  which  was  lost  during  some  former 
generation,  this  tendency,  for  all  that  we  can  see  to  the  contrary, 
may  be  transmitted  imdiminishcd  for  an  indefinite  nunil)er  of 
generations.  These  two  distinct  cases  of  reversion  are  often 
confounded  together  by  those  who  have  Avritten  on  inheritance. 

Lastly,  the  hybrids  or  mongrels  from  between  all  the 
domestic  breeds  of  pigeons  are  perfectly  fertile.  I  can  state 
this  from  my  own  oljservationR,  purposely  made,  on  the  most 
distinct  breeds.  Now,  it  is  diflicult,  perhaps  impossible,  to 
bring  forward  one  case  of  the  hybrid  offspring  of  two  animals 
clenrbj  distbict  being  themselves  perfectly  fertile.  Some 
authors  believe  that  long-continu(?d  domestication  eliminates 
this  strong  tendency  to  sterilily:  from  the  histor}' of  tlie  dog, 
and  of  some  other  domestic  animals,  there  is  great  probability 
in  this  hypothesis,  if  applied  to  species  closely  related  to  each 
other,  thougli  it  is  imsupported  by  a  single  experiment.  But 
A.O  extend  the  h^11otIlesis  so  far  as  to  suppose  that  sjx'cies, 
aboriginally  as  distinct  as  carriers,  tumblers,  pouters,  and  fan- 
tails  now  are,  should  yield  offspring  perfectly  fertile  inter  se^ 
seems  to  me  rash  in  the  extreme. 

From  these  several  reasons,  namely,  the  improbability  of 


38  DOMESTIC  PIGEONS.  Chap.  I. 

man  having  formerly  got  seven  or  eight  supposed  species  of 
pigeons  to  breed  freely  under  domestication ;  these  supposed 
species  being  quite  unknown  in  a  ■wild  state,  and  their  be- 
coming nowhere  feral ;  these  species  having  very  al^normal 
characters  in  certain  respects,  as  conijoared  with  all  other  Co- 
lumbida?,  thougli  so  like  in  most  other  respects  to  the  rock- 
pigeon  ;  the  bkic  color  and  various  black  marks  occasionally 
apjiearing  in  all  the  breeds,  both  when  kept  pure  and  when 
crossed ;  the  mongrel  offspring  being  perfectly  fertile — from 
these  several  reasons,  taken  together,  we  may  safely  conclude 
that  all  our  domestic  breeds  have  descended  from  the  Columba 
livia  Avith  its  geographical  sub-species. 

In  favor  of  this  view,  I  may  add,  first,  that  C.  livia,  or  the 
rock-pigeon,  has  been  found  capable  of  domestication  in  Europe 
and  in  India  ;  and  that  it  agrees  in  habits  and  in  a  great  num- 
ber of  points  of  structure  with  all  the  domestic  breeds.  Second- 
ly, although  an  English  carrier  or  a  short-faced  tumbler  differs 
immensely  in  certain  characters  from  the  rock-pigeon,  yet  by 
comparing  the  several  sub-breeds  of  these  varieties,  more 
especially  those  brought  from  distant  countries,  we  can  make 
in  these  two  cases,  and  in  some  but  not  in  all  other  cases, 
an  almost  perfect  series  between  the  extremes  of  stlncture. 
Thirdly,  those  characters  which  are  mainly  distinctive  of  each 
breed,  for  instance  the  wattle  and  length  of  beak  of  the  car- 
rier, the  shortness  of  that  of  the  tumbler,  and  the  number  of 
tail-feathers  in  the  fantail,  ai'C  in  each  breed  eminently  variable; 
and  the  explanation  of  this  fact  Avill  be  obvious  Avhcn  we  come 
to  treat  of  Selection.  Fourthly,  pigeons  have  been  Avatched 
and  tended  Avith  the  utmost  care,  and  loved  by  many  people. 
They  liaA'C  been  domesticated  for  thousands  of  years  in  several 
quarters  of  the  Avorld ;  the  earliest  knoAvn  record  of  pigeons 
is  in  the  fifth  Eg^-ptian  dynasty,  about  3000  B.  c,  as  Avas 
pointed  out  to  me  by  Prol;  Lcpsius ;  but  Mr.  Birch  informs 
me  that  pigeons  are  given  in  a  bill  of  fare  in  the  previous 
dynasty.  In  the  time  of  the  Romans,  as  AA'e  hear  from  Pliny, 
immense  prices  Averc  giAxn  for  pigeons ;  "  nay,  they  are  come 
to  this  pass,  that  they  can  reckon  up  their  pedigree  and  race." 
Pigeons  Avere  much  A'alued  by  Akbar  Ivlian  in  India,  about 
the  j-ear  IGOO;  never  less  than  20,000  pigeons  Avere  taken 
Avith  the  tourt.  "  The  monarchs  of  Iran  and  Turan  sent  him 
some  very  rare  birds;"  and,  continues  the  courtly  historian, 
"  his  Majesty  by  crossing  the  breeds,  Avhich  method  Avas  ncA'cr 
practised  before,  has  improved  them  astonishingly."     About 


Chap.  I.  DOMESTIC   PIGEONS.  39 

this  saino  period  the  Dutch  were  as  easier  about  pigeons  as 
were  the  old  Romans.  The  paramount  importance  of  these 
considerations  in  explainini^  the  immense  amount  of  variation 
Avhich  pigeons  have  undcr2;one,  will  be  obvious  when  Ave  treat 
of  Selection.  We  shall  then,  also,  see  how  it  is  that  the 
several  breeds  so  often  have  a  somewhat  monstrous  character. 
It  is  also  a  most  favorable  circumstance  for  the  production  of 
distinct  breeds,  that  male  and  female  pigeons  can  be  easily 
mated  for  life ;  and  thus  different  breeds  can  be  kept  together 
in  the  same  aviary. 

I  have  discussed  tlie  probable  origin  of  domestic  pigeons 
at  some,  yet  quite  insufiieient,  length ;  because  when  I  first 
kept  pigeons  and  watched  the  several  kinds,  avcU  knowing  how 
truly  they  breed,  I  felt  fully  as  mucli  dilliculty  in  believing 
that  since  they  had  been  domesticated  they  had  all  proceeded 
from  a  common  parent,  as  any  naturalist  could  in  coming  to 
a  similar  conclusion  in  regard  to  the  many  species  of  finches, 
or  other  groups  of  birds,  in  nature.  One  circumstance  has 
struck  me  much ;  namely,  that  nearly  all  the  breeders  of  the 
various  domestic  animals  and  the  cultivators  of  plants,  v/ith 
whom  I  have  conversed,  or  Avhose  treatises  I  have  read,  are 
firmly  convinced  that  the  several  breeds  to  Avhich  each  has 
attended,  are  descended  from  so  many  aboriginally  distinct 
species.  Ask,  as  I  have  asked,  a  celebrated  raiser  of  Here- 
ford cattle,  whether  his  cattle  might  not  have  descended  from 
Long-horns,  or  both  from  a  common  parent-stock,  and  he  Avill 
laugh  you  to  scorn,  I  have  never  met  a  pigeon,  or  })oultry, 
or  duck,  or  rabljit  fancier,  Avho  was  not  fully  convinced  that 
each  main  breed  was  descended  from  a  distinct  species.  Van 
Mons,  in  his  treatise  on  pears  and  apples,  shows  how  utterly 
he  disbelieves  that  tlie  several  sorts,  for  instance  a  Ribston- 
pippin  or  Codlin-apple,  could  ever  have  proceeded  from  the 
seeds  of  the  same  tree.  Innumerable  other  examples  could 
be  given.  The  explanation,  I  think,  is  simple :  from  long- 
continued  study  they  are  strongly  impressed  with  the  differ- 
ences between  the  several  races ;  and  though  they  well  know 
that  each  race  varies  slightly,  for  they  win  their  prizes  by 
selecting  such  slight  differences,  yet  they  ignore  all  general 
arguments,  and  refuse  to  sum  u[)  in  their  minds  slight  differ- 
ences accumulated  during  many  successive  generations.  May 
not  those  naturalists  who,  knowing  far  less  of  the  laws  of 
inheritance  than  does  the  breeder,  and  knowing  no  more  than 
be  docs  of  the  intermediate  links  in  the  long  lines  of  descent, 


40  SELECTION   BY   MAN.  Cn.sr.  I. 

yet  admit  that  many  of  our  domestic  races  are  descended  from 
the  same  parents — may  they  not  learn  a  lesson  of  caution, 
when  tlicy  deride  the  idea  of  species  in  a  state  of  nature  being 
lineal  descendants  of  other  species  ? 

Princi2>les  of  Selection  anciently  foUoiccd,  and  their  Effects. 

r^et  us  now  briefly  consider  the  steps  by  which  domestic 
races  have  been  produced,  either  from  one  or  from  several 
allied  species.  Some  elTect  may  be  attributed  to  the  direct 
and  definite  action  of  the  external  conditions  of  life,  and  some 
little  to  habit ;  but  he  would  be  a  bold  man  who  would  ac- 
count by  such  agencies  for  the  differences  between  a  dray  and 
race  horse,  a  greyhound  and  bloodhound,  a  carrier  and  tumbler 
jiigeon.  One  of  the  most  remarkable  features  in  our  domesti- 
cated races  is  that  we  see  in  them  adaptation,  not  indeed  to  the 
animal's  or  plant's  own  good,  but  to  man's  use  or  fancy.  Some 
variations  useful  to  him  have  probably  arisen  suddenl}-,  or  by 
one  step  ;  many  botanists,  for  instance,  ])elieve  that  the  fuller's 
teasel,  with  its  hooks,  which  cannot  be  rivalled  by  any  mechan- 
ical contrivance,  is  only  a  variety  of  the  wild  Dipsacus ;  and 
this  amount  of  change  may  have  suddenly  arisen  in  a  seedling. 
So  it  has  probably  been  with  tlie  turnspit-tlog ;  and  tliis  is 
known  to  have  been  the  case  with  the  ancon  sheep.  But  when 
we  compare  the  dray-horse  and  race-horse,  the  dromedary  and 
camel,  the  various  breeds  of  sheep  fitted  either  for  cultivated 
land  or  mountain-pasture,  with  the  wool  of  one  breed  good  for 
one  purpose,  and  that  of  another  breed  for  another  purpose ; 
when  we  compare  the  many  breeds  of  dogs,  each  good  for  man 
in  very  different  ways ;  when  we  compare  the  game-cock,  so 
pertinacious  in  battle,  with  other  breeds  so  little  quarrelsome, 
with  "everlasting  layers"  which  never  desire  to  sit,  and  Avith 
the  bantam  so  small  and  elegant ;  w^hen  we  compare  the  host 
of  agricultural,  culinary,  orchard,  and  flower-garden  races  of 
plants,  most  useful  to  man  at  dillerent  seasons  and  for  differ- 
ent purposes,  or  so  beautiful  in  his  eyes,  we  must,  I  think, 
look  fi'rther  than  to  mere  variability.  "We  cannot  sup]")ose 
that  all  the  breeds  were  suddenly  produced  as  perfect  and  as 
useful  as  we  now  see  them ;  indeed,  in  many  cases,  we  know 
that  this  has  not  been  their  history.  The  key  is  man's  ])ower 
of  accumulative  selection:  Nature  gives  successive  variations; 
man  a<lds  them  up  in  certain  directions  useful  to  him.  In  tliig 
sense  he  may  be  said  to  have  made  for  himself  useful  breeds. 


Chap.  I.  SELECTION  BY  MAN.  41 

Tlie  great  poAVcr  of  tliis  j^rinciple  of  selection  is  not  hj- 
potlietical.  It  is  certain  that  several  of  our  eminent  breeders 
nave,  even  within  a  single  lifetime,  modilied  to  a  large  extent 
the  breeds  of  cattle  and  sheep.  In  order  fully  to  realize  -what 
they  have  done,  it  is  almost  necessary  to  read  several  of  the 
many  treatises  devoted  to  this  subject,  and  to  inspect  the  ani- 
mals. Breeders  habitually  speak  of  an  animal's  organization 
as  something  quite  plastic,  which  they  can  model  almost  as 
thcv  please.  If  I  had  space  I  could  quote  numerous  passages 
to  this  effect  from  highly-competent  authorities.  Youatt,  -who 
was  probably  better  acquainted  with  the  works  of  agricultu- 
rists than  almost  any  other  individual,  and  who  was  himself  a 
very  good  judge  of  an  animal,  speaks  of  the  principle  of  selec- 
tion as  "  that  Avliich  enables  the  agriculturist,  not  only  to  mod- 
ify the  character  of  his  flock,  but  to  change  it  altogether.  It 
is  the  magician's  wand,  by  means  of  which  he  may  summon 
into  life  whatever  form  and  mould  he  pleases."  Lord  Somer- 
ville,  speaking  of  what  breeders  have  done  for  sheep,  says  : 
"  It  would  seem  as  if  they  had  chalked  out  upon  a  -wall  a  form 
perfect  in  itself,  and  then  had  given  it  existence."  In  Saxony 
the  importance  of  the  principle  of  selection  in  regard  to  merino 
sheep  is  so  fully  recognized,  that  men  follow  it  as  a  trade :  the 
sheep  are  placed  on  a  table  and  arc  studied,  like  a  picture  by 
a  connoisseur  ;  this  is  done  three  times  at  intervals  of  months, 
and  the  sheep  are  each  time  marked  and  classed,  so  that  the 
very  best  may  ultimately  be  selected  for  breeding. 

What  English  breeders  have  actually  eifectecl  is  proved  by 
the  enormous  prices  given  for  animals  with  a  good  pedigree  ; 
and  these  have  now  been  exported  to  almost  every  quarter  of 
the  world.  The  imjirovement  is  by  no  means  generally  due 
to  crossing  diilerent  breeds ;  all  the  best  breeders  are  strongly 
opposed  to  this  practice,  except  sometimes  among  closely-al- 
lied sub-breeds.  And  when  a  cross  has  been  made,  the  closest 
selection  is  far  more  indispensable  even  than  in  ordinary  cases. 
If  selection  consisted  merely  in  separating  some  very  distinct 
variety,  and  breeding  from  it,  the  princi^Dlc  would  be  so  obvi- 
ous as  liardly  to  be  worth  notice  ;  but  its  imjiortance  consists 
in  the  great  edec't  produced  by  tlie  accumulation  in  one  direc- 
tion, during  successive  generations,  of  diiferences  absolutely 
inappreciable  by  an  imeducated  e^-c — diflerences  which  I  for 
one  have  vainly  attempted  to  appreciate.  Not  one  man  in  a 
thousand  has  accuracy  of  eye  and  judgment  sufficient  to  be- 
come an  eminent  breeder.     If  gifted  with  these  qualities,  and 


io  SELECTION  BY  MAN.  Ca.vr.  1, 

lie  studies  his  subject  for  years,  and  devotes  his  lifetime  to  it 
witli  indomitable  ])erscverance,  he  "sviU  succeed,  and  may  make 
great  improvements  ;  if  he  wants  any  of  these  qualities,  he  aa'III 
assuredly  fail.  Few  -would  readily  believe  in  the  natural  ca- 
pacity and  years  of  practice  requisite  to  become  even  a  skilful 
pigeon-fancier. 

The  same  principles  are  followed  by  horticulturists  ;  but  the 
variations  are  here  often  more  abrupt.  No  one  supposes  that 
our  choicest  productions  have  been  produced  by  a  single  vari- 
ation from  the  aboriginal  stock.  "W^e  have  proofs  that  this  is 
not  so  in  some  cases  in  Avhich  exact  records  have  been  kept : 
thus,  to  give  a  very  trifling  instance,  the  steadily-increasing 
size  of  the  common  gooseberry  may  be  quoted.  We  see  an 
astonishing  improvement  in  many  florists'  flowers,  when  the 
flowei'S  of  the  present  day  are  compared  with  drawings  made 
only  twenty  or  thirty  years  ago.  When  a  race  of  plants  is 
once  pretty  Avell  established,  the  seed-raisers  do  not  pick  out 
the  best  plants,  but  merely  go  over  their  seed-beds,  and  pull 
up  the  "  rogues,"  as  they  call  the  plants  that  deviate  from  the 
]iroper  standard.  With  animals  this  kind  of  selection  is,  in 
fact,  also  followed ;  for  hardly  any  one  is  so  careless  as  to 
allow  his  Avorst  animals  to  breed. 

In  regard  to  plants,  there  is  another  means  of  observing  the 
accmnulated  effects  of  selection — namely,  by  comparing  the 
diversity  of  flowers  in  the  different  varieties  of  the  same  species 
in  the  flower-garden ;  the  diversity  of  leaves,  pods,  or  tubers, 
or  whatever  part  is  valued,  in  the  kitchen-garden,  in  compari- 
son with  the  flowers  of  the  same  varieties ;  and  the  diversity 
of  fruit  of  the  same  species  in  the  orchard,  in  comparison  with 
the  leaves  and  flowers  of  the  same  set  of  varieties.  See  how 
different  the  leaves  of  the  cabbage  are,  and  how  extremely 
alike  the  flowers ;  how  unlike  the  flowers  of  the  heart's-ease 
are,  and  how  alike  the  leaves ;  how  much  the  fruit  of  the  dif- 
ferent kinds  of  gooseberries  differ  in  size,  color,  shape,  and 
hairiness,  and  yet  the  flowers  present  very  slight  differences. 
It  is  not  that  tlie  varieties  which  differ  largely  in  some  one 
point  do  not  differ  at  all  in  other  points  ;  this  is  hardly  ever — 
I  speak  after  careful  observation — perhaps  never,  the  case. 
Tlie  law  of  correlated  variation,  the  importance  of  which  should 
never  be  overlooked,  will  insure  some  diflerences ;  but,  as  a 
general  rule,  I  cannot  doul)t  that  the  continued  selection  of 
slight  v:iriations,  either  in  the  leaves,  the  flowers,  or  the  fruit, 
will  produce  races  dillering  from  each  other  chiefly  in  these 
characters. 


Chap.  I  UNCONSCIOUS  SELECTION.  43 

It  may  be  objected  that  the  principle  of  selection  has  been 
reduced  to  methodical  practice  ibr  scarcely  more  than  three- 
quarters  of  a  century  ;  it  has  certainly  been  more  attended  to 
of  late  years,  and  many  treatises  have  been  published  on  the 
subjc^ct ;  and  the  result  has  been,  in  a  correspondinjr  degree,  rapid 
and  important.  But  it  is  very  far  from  true  that  the  jjrinciple  is 
a  modern  discovery.  I  could  give  several  references  to  the  full 
acknowledgment  of  the  importance  of  the  principle  in  woiks 
of  higli  anti(iuity.  In  rude  and  barbarous  periods  of  English 
history,  choice  animals  -were  often  imported,  and  laws  were 
passed  to  prevent  their  exportation :  the  destruction  of  horses 
imdcr  a  certain  size  was  ordered,  and  this  may  be  comjiared 
to  tlic  "  roguing  "  of  plants  by  nurserymen.  Tlic  principle  of 
selection  1  lind  distinctly  given  in  an  ancient  Chinese  encyclo- 
pajdia.  Exjilicit  rules  are  laid  down  by  some  of  the  Roman 
classical  writers.  From  passages  in  Genesis,  it  is  clear  that 
the  color  of  domestic  animals  was  at  that  early  period  attended 
to.  Savages  now  sometimes  cross  their  dogs  with  wild  canine 
animals,  to  improve  the  breed,  and  they  formerly  did  so,  as  is 
attested  by  passages  in  Pliny.  The  savages  in  South  Africa 
match  their  draught^cattle  by  color,  as  do  some  of  the  PJsqui- 
maux  their  teams  of  dogs.  Livingstone  states  that  good  do- 
mestic breeds  arc  highly  valued  by  the  negroes  in  the  interior 
of  Africa  who  have  not  associated  with  Euroj^eans.  Some  of 
these  facts  do  not  show  actual  selection,  but  they  show  that 
the  breeding  of  domestic  animals  was  carefully  attended  to  in 
ancient  times,  and  is  now  attended  to  by  the  lowest  savages. 
It  would,  indeed,  have  been  a  strange  fact,  had  attention  not 
been  paid  to  breeding,  for  the  inheritance  of  good  and  bad 
qualities  is  so  obvious. 

Unconscious  Selection. 

At  the  present  time,  eminent  breeders  try  by  methodical 
selection,  with  a  distinct  object  in  view,  to  make  a  new  strain 
or  sul>breed,  superior  to  any  thing  existing  in  the  country. 
But,  for  our  purpose,  a  kind  of  Selection,  which  may  be  called 
Unconscious,  and  which  results  frojn  every  one  trying  to  pos- 
sess and  breed  from  the  best  individual  animals,  is  more  im- 
portant. Thus,  a  man  who  intends  keeping  pointere  naturally 
tries  to  get  as  good  dogs  as  he  can,  and  afterward  breeds  from 
his  own  best  dogs,  but  he  has  no  wish  or  exjiectation  of  per- 
manently altering  the  breed.     Nevertheless,  we  may  infer  that 


(4  DNCONSCIOUS  SELECTION.  Ciiai-.  I. 

Iliis  process,  continued  during  centuries,  Avould  improve  and 
modify  any  I)recd,  in  the  same  "way  as  Bakeivell,  Collins,  etc., 
by  this  very  same  process,  only  carried  on  more  metliodically, 
did  greatly  modify,  even  during  their  own  lifetimes,  the  forms 
and  qualities  of  their  cattle.  Slow  and  insensible  changes  of 
this  kind  could  never  be  recognized  unless  actual  measure- 
ments or  careful  drawings  of  the  breeds  in  cjuestion  had  been 
made  long  ago,  which  might  serve  for  comparison.  In  some 
cases,  however,  imchanged  or  but  little  changed  individuals 
of  the  same  breed  may  be  found  in  less  civilized  districts, 
Avhere  the  breed  has  been  less  improved.  There  is  reason  to 
believe  that  King  Charles's  spaniel  has  been  unconsciously 
modified  to  a  large  extent  since  the  time  of  that  monarch. 
Some  highly-competent  authorities  are  convinced  that  the 
setter  is  directly  derived  from  the  spaniel,  and  has  probably 
been  slowly  altered  from  it.  It  is  known  that  the  English 
pointer  has  been  greatly  changed  within  the  last  century,  and 
in  this  case  the  change  has,  it  is  believed,  been  chiefly  elfected 
by  crosses  Avith  the  fox-hound ;  but  what  concerns  us  is,  that 
the  change  has  ]:)ccn  elTccted  unconsciously  and  gradually,  and 
yet  so  eifectually,  that,  thougli  the  old  Spanish  pointer  cer- 
tainly came  from  Spain,  Mr.  Boitow  has  not  seen,  as  I  am 
informed  by  him,  any  native  dog  in  Spain  like  our  pointer. 

By  a  similar  process  of  selection,  and  by  careful  training, 
the  whole  body  of  English  race-horses  have  come  to  surpass 
in  fleetness  and  size  the  parent  Arab  stock,  so  that  the  latter, 
1)}'  the  regulations  for  the  Goodwood  Races,  are  favored  in  the 
Aveights  tlicy  carry.  Lord  Sjicncer  and  others  have  shown 
how  the  cattle  of  England  have  increased  in  weight  and  in 
early  maturity,  compared  with  the  stock  formerly  kept  in  this 
country.  By  comparing  the  accounts  given  in  old  pigeon 
treatises  of  carriers  ami  tumblers  with  these  breeds  as  now 
existing  in  Britain,  India,  and  Persia,  Ave  can,  I  think,  clearly 
trace  the  stages  through  Avhich  they  have  insensibly  passed, 
and  come  to  dilfer  so  greatly  from  the  rock-pigeon. 

Youatt  gives  an  excellent  illustration  of  the  effects  of  a 
course  of  selection,  AA-hich  may  be  considered  as  unconsciously 
followed,  in  so  far  that  the  breeders  could  never  have  expect- 
ed, or  even  have  A\ished,  to  produce  the  result  Avliich  ensueil — 
namely,  the  production  of  tAvo  distinct  strains.  The  two  Hocks 
of  Leicester  sheep  ke])t  by  Mr.  Buckley  and  INIr.  Burgess,  as 
Mr.  Youatt  remarks,  "  have  been  purely  bred  from  the  original 
stock  of  Mr.  Bakewell  for  upAvard  of  lifty  years.     There  is  not 


Ci.vr.  I.  UNCONSCIOUS  SELECTION.  45 

a  suspicion  existing  in  the  mind  of  any  one  at  all  acquainted 
with  the  subject,  that  the  owner  of  cither  of  them  has  deviated 
in  any  one  instance  from  tlie  pure  blood  of  Mr.  BakewcU's 
flock,  and  yet  the  difference  between  tlie  sheep  possessed  by 
these  two  f^entlemen  is  so  f^reat  that  they  have  the  appear- 
ance of  being  quite  difl'erent  varieties." 

If  there  exist  savages  so  barbarous  as  never  to  think  of 
the  inherited  character  of  the  offspring  of  their  domestic  ani- 
mals, yet  any  one  animal  particularly  useful  to  them,  for  any 
special  purpose,  would  be  carefully  preserved  during  famines 
and  other  accidents,  to  Avhich  savages  are  so  liable,  and  such 
choice  animals  would  thus  generally  leave  more  offspring  than 
the  inferior  ones ;  so  that  in  this  case  there  would  be  a  kind  * 
of  unconscious  selection  going  on.  We  see  the  value  set  on 
animals  even  by  the  barbarians  of  Tierra  del  Fuego,  by  their 
killing  and  devouring  their  old  women,  in  times  of  dearth,  as 
of  less  value  than  their  dogs. 

In  plants  the  same  gradual  process  of  improvement,  through 
the  occasional  preservation  of  the  best  indi\4duals,  whether  or 
not  sufBciently  distinct  to  be  ranked  at  their  first  appearance 
as  distinct  varieties,  and  whether  or  not  two  or  more  species 
or  races  have  become  blended  together  by  crossing,  may  plainly 
be  recognized  in  the  increased  size  and  beauty  which  we  now 
see  in  the  varieties  of  the  heart's-easo,  rose,  pelargonium, 
dahlia,  and  other  plants,  when  compared  \\-ith  the  older  varie- 
ties or  with  their  parent-stocks.  No  one  would  ever  expect 
to  get  a  first-rate  heart's-ease  or  dahlia  from  the  seed  of  a  wild 
plant.  No  one  would  expect  to  raise  a  first-rate  melting  ]jear 
from  the  seed  of  the  wild  pear,  though  he  might  succeed  from 
a  poor  seedling  growing  wild,  if  it  had  come  from  a  garden- 
stock.  The  pear,  though  cultivated  in  classical  times,  appears, 
from  Pliny's  description,  to  have  been  a  fruit  of  very  inferior 
quality.  I  have  seen  great  surprise  expressed  in  horticultm-al 
works  at  the  wonderful  skill  of  gardeners,  in  having  produced 
such  splendid  results  from  such  poor  materials ;  but  the  art 
has  been  simple,  and,  as  far  as  tlie  final  result  is  concerned, 
lias  been  followed  almost  unconsciously.  It  has  consisted  in 
always  cultivating  the  best-known  variety,  sowing  its  seeds, 
antl,  when  a  sliglitly-better  variety  has  chanced  to  appear, 
selecting  it,  and  so  onward.  But  the  gardeners  of  the  classi- 
cal period,  who  cultivated  the  best  pear  they  could  procure, 
never  thought  Avhat  splendid  fruit  we  should  eat;  though  wo. 
owe  our  excellent  fruit,  in  some  small  degree,  to  their  having 


to  UNCONSCIOUS  SELECTION.  Chap.  I. 

naturally  chosen  and  preserved  the  best  varieties  they  could 
anywhere  inid. 

A  laro-e  amount  of  chang'c  in  our  cultivated  plants,  thus 
slowly  and  unconsciously  accumulated,  explains,  as  I  believe, 
the  well-known  fact  that,  in  a  number  of  cases,  we  cannot 
recognize,  and  therefore  do  not  know,  the  wild  parent-stocks 
of  the  plants  which  have  been  longest  cultivated  in  our  flower 
and  kitchen  gardens.  If  it  has  taken  centuries  or  thousands 
of  3'^ears  to  improve  or  modify  most  of  our  plants  up  to  their 
present  standard  of  usefulness  to  man,  we  can  understand  how 
it  is  that  neither  Australia,  the  Cape  of  Good  Hope,  nor  any 
other  region  inhabited  by  quite  uncivilized  man,  has  aiforded  us 
a  single  plant  worth  culture.  It  is  not  that  these  countries,  so 
rich  in  species,  do  not  by  a  strange  chance  possess  the  abori- 
ginal stocks  of  any  useful  plants,  but  that  the  native  plants 
have  not  been  improved  by  continued  selection  up  to  a  stand- 
ard of  perfection  comparable  with  that  given  to  tiie  plants  in 
countries  anciently  civilized. 

In  regard  to  the  domestic  animals  kept  by  uncivilized  man, 
it  should  not  be  overlooked  that  they  almost  always  have  to 
struggle  for  their  own  food,  at  least  during  certain  seasons. 
And,  in  two  countries  very  diifcrently  circumstanced,  individ- 
\ials  of  the  same  species,  having  slightly-different  constitutions 
or  structure,  would  often  succeed  better  in  the  one  country 
than  in  the  other;  and  thus  by  a  process  of  "natural  selec- 
tion," as  will  hereafter  be  more  fully  explained,  two  sub-breeds 
might  be  formed.  This,  perhaps,  partly  explains  Avhat  has 
been  remarked  by  soiiic  authors,  namely,  that  the  varieties 
kept  by  savages  have  more  of  the  character  of  species  than 
the  varieties  kept  in  civilized  countries. 

On  the  view  here  given  of  the  all-important  part  which 
selection  by  man  has  played,  it  becomes  at  once  ob\-ious  how 
it  is  that  our  domestic  races  show  adaptation  in  their  stnicture 
or  in  their  habits  to  man's  wants  or  fancies.  We  can,  I  think, 
further  understand  the  frequently-abnormal  character  of  our 
domestic  races,  and  likewise  their  differences  being  so  great 
in  external  characters,  and  relatively  so  slight  in  internal  parts 
or  organs.  Man  can  hardly  select,  or  only  with  much  dilhculty, 
any  deviation  of  structure,  excepting  such  as  is  externally  vis- 
ible ;  and  indeed  he  rarely  cares  for  what  is  internal.  He  can 
never  act  l)y  selection,  excepting  on  variations  which  are  first 
given  to  him  in  some  slight  degree  by  Nature.  No  man  would 
ever  try  to  make  a  fantail  till  he   saw  a  pigeon  with  a  tail  de- 


CiiAr.  I.  UNCONSCIOUS  SELECTION.  47 

veloped  in  some  slis^lit  degree  in  an  unusual  manner,  or  a 
pouter  till  lie  saw  a  pi<j^eon  -with  a  crop  of  somewhat  unusual 
size  ;  and  the  more  abnormal  or  unusual  any  character  was 
when  it  first  appeared,  the  more  likely  it  would  be  to  catch  his 
attention.  But  to  use  such  an  expression  as  trying  to  make 
a  fantail,  is,  I  have  no  doubt,  in  most  cases,  utterly  incorrect. 
The  man  Avho  first  selected  a  pigeon  with  a  slightly-larger 
tail,  never  dreamed  what  the  descendants  of  that  pigeon  would 
ht'come  through  long-continued,  partly-unconscious  and  parti  y- 
nicthodical  selection.  Perhaps  the  parent-bird  of  all  fantails 
had  only  fourteen  tail-feathers  somewhat  expanded,  like  the 
jircsent  Java  fantail,  or  like  individuals  of  other  and  distinct 
breeds,  in  which  as  many  as  seventeen  tail-feathers  have  been 
counted.  Perhaps  tlie  first  pouter-pigeon  did  not  inflate  its 
crop  much  more  than  the  turbit  now  does  the  upper  part  of  its 
ccsojihagus-^a  habit  which  is  disregarded  by  aU  fanciers,  as  it 
is  not  one  of  the  points  of  the  breed. 

Nor  let  it  be  thought  that  some  great  de\'iation  of  struc- 
ture would  be  necessary  to  catch  the  fancier's  eye  :  he  per- 
ceives extremely-small  differences,  and  it  is  in  human  nature  to 
value  any  novelty,  however  slight,  in  one's  own  possession. 
Nor  must  the  value  which  would  formerly  be  set  on  any  slight 
differences  in  the  individuals  of  the  same  species,  be  judged  of 
by  the  value  which  would  now  be  set  on  them,  after  several 
])reeds  have  once  fairly  been  established.  Many  slight  differ- 
ences might,  and  indeed  do  now,  arise  among  pigeons,  which 
are  rejected  as  faults  or  deviations  from  the  standard  of  per- 
fection of  each  breed.  The  common  goose  has  not  given  rise 
to  any  marked  varieties;  hence  the  Toulouse  and  the  common 
breed,  Avhich  differ  only  in  color,  that  most  fleeting  of  char- 
acters, have  lately  been  exhibited  as  distinct  at  our  poultry- 
shows. 

I  think  those  views  explain  what  has  sometimes  been 
noticed — namely,  that  we  know  nothing  about  the  origin  or 
history  of  any  of  our  domestic  breeds.  But,  in  fact,  a  breed, 
like  a  dialect  of  a  language,  can  hardly  be  said  to  have  a  dis- 
tinct origin.  A  man  preserves  and  breeds  from  an  individual 
with  some  slight  deviation  of  structure,  or  takes  more  care  than 
usual  in  matching  his  best  animals,  and  thus  imjiroves  them, 
and  the  improved  animals  slowly  spread  in  the  immediate 
neighborhood.  But  as  yet  they  will  hardly  have  a  distinct 
name,  and,  from  being  only  slightly  valued,  their  history  will 
be  disregardt>d,     ^^''hen  further   improved  by  the  same  slow 


48  CIRCUMSTANCES  FAVORABLE  TO  SELECTION.     Chap.  I. 

and  gradual  process,  tliey  will  spread  more  widely,  and  will  get 
recognized  as  sometliing  distinct  and  valuable,  and  will  then 
probably  first  receive  a  provincial  name.  In  semi-civilized 
countries,  with  little  free  communication,  the  spreading  of  a 
new  sub-breed  would  be  a  slow  process.  As  soon  as  the  points 
of  value  in  a  new  strain  are  once  acknowledged,  the  principle, 
as  I  have  called  it,  of  unconscious  selection  will  always  tend — per- 
haps more  at  one  period  than  at  another,  as  the  breed  rises  or 
falls  in  fashion — perhaps  more  in  one  district  than  in  another, 
according  to  the  state  of  civilization  of  the  inhabitants — slowly 
to  add  to  the  characteristic  features  of  the  breed,  whatever 
they  may  be.  But  the  chance  may  be  infinitely  small  of  any 
record  having  been  jireserved  of  such  slow,  varying,  and  insen- 
sible changes. 

Circumstances  favorable  to  Mail's  Power  of  Selection. 

I  must  now  say  a  few  words  on  the  circumstances,  favor- 
able, or  the  reverse,  to  man's  power  of  selection.  A  high  de- 
gree of  variability  is  obviously  favorable,  as  freely  giving  the 
materials  for  selection  to  work  on  ;  not  that  mere  individual 
differences  are  not  amply  sufficient,  with  extreme  care,  to  allow 
of  the  accumulation  of  a  large  amount  of  modification  in  almost 
any  desired  direction.  But,  as  variations  manifestly  useful  or 
pleasing  to  man  appear  only  occasionally,  the  chance  of  their 
appearance  will  be  much  increased  by  a  large  number  of  indi- 
viduals being  kept ;  and  hence  tliis  comes  to  be  of  the  highest 
importance  to  success.  On  this  principle  Marshall  formerly 
remarked,  with  respect  to  the  sheep  of  parts  of  Yorkshu-e,  that, 
"  as  they  generally  belong  to  poor  people,  and  are  mostly  in 
small  lots,  they  never  can  l)e  improved."  On  the  other  hand, 
nurservmen,  from  raising  large  stocks  of  the  same  plants,  arc 
generally  far  more  successful  than  amateurs  in  getting  new 
and  valuable  varieties.  The  keejiing  of  a  large  number  of  in- 
dividuals of  a  species  in  any  country  requires  that  the  species 
should  be  placed  under  favorable  conditions  of  life,  so  as  to 
breed  freely  in  that  countr>',  A\^hcn  the  indi\'iduals  of  any 
species  are  scanty,  all  the  individuals,  whatever  their  quality 
may  be,  will  generally  be  allowed  to  l)reed,  and  this  will  effect- 
ually prevent  selection.  But  probably  the  most  important 
point  of  all  is,  that  the  animal  or  plant  should  be  so  highly 
useful  to  man,  or  so  much  valued  hy  him,  that  tlie  closest  at- 
Irntion  is  paid  to  even  the  slightest  dmiation  in  the  qualities 


Chap.  I.    CIRCUMSTANCES  FAVORABLE  TO  SELECTION.  49 

or  structure  of  each  individual.  Unless  such  attention  be  paid 
nothinf^  can  be  effected.  I  have  seen  it  gravely  remarked,  that 
it  was  most  fortimate  that  tlic  strawberry  began  to  vary  just 
when  gardeners  began  to  attend  closely  to  this  plant.  No  doubt 
the  strawberry  had  always  varied  since  it  was  cultivated,  but 
the  slight  varieties  had  been  neglected.  As  soon,  however, 
as  gardeners  picked  out  individual  plants  with  slightly  larger, 
earlier,  or  better  fruit,  and  raised  seedlings  from  them,  and 
again  })ickcd  out  the  best  seedlings  and  bred  from  them,  then, 
there  appeared  (aided  by  some  crossing  with  distinct  species) 
those  many  admirable  varieties  of  the  strawberry  which  have 
been  raised  during  the  last  thirty  or  forty  years. 

In  the  case  of  animals  with  separate  sexes,  facility  in  pre- 
venting crosses  is  an  important  element  of  success  in  the  for- 
mation of  new  races — at  least,  in  a  country  which  is  already 
stocked  with  -other  races.  In  this  respect,  enclosure  of  the 
land  plays  a  part.  Wandering  savages  or  the  inhabitants  of 
open  plains  rarely  possess  more  than  one  breed  of  the  same 
species.  Pigeons  can  be  mated  for  life,  and  this  is  a  great 
convenience  to  the  fancier,  for  thus  many  races  may  be  im- 
proved and  kept  true,  though  mingled  in  the  same  aviary ;  and 
this  circumstance  must  have  largely  favored  the  formation  of 
new  breeds.  Pigeons,  I  may  add,  can  be  propagated  in  great 
numbers  and  at  a  very  quick  rate,  and  inferior  birds  may  be 
freely  rejected,  as  when  killed  tliey  serve  for  food.  On  the 
other  hand,  cats,  from  their  nocturnal  rambling  habits,  cannot 
be  easily  matched,  and,  although  so  much  valued  by  women 
and  children,  we  hardly  ever  see  a  distinct  breed  kept  up  ;  such 
breeds  as  we  do  sometimes  sec  are  iilmost  always  imported 
from  some  other  country.  Although  I  do  not  doubt  that  some 
domestic  animals  vary  less  than  others,  yet  the  rarity  or  ab- 
sence of  distinct  l)reeds  of  the  cat,  the  donkey,  peacock,  goose, 
etc.,  may  be  attril)uted  in  main  part  to  selection  not  having 
been  l)rought  into  play  :  in  cats,  from  tlie  difhculty  in  pairing 
them  :  in  donkeys,  from  onl}'^  a  few  ])oing  kept  by  poor  jieople, 
and  little  attention  paid  to  their  breeding;  for  recently,  in  cer- 
tain parts  of  Spain  and  of  the  United  States,  tliis  animal  has 
been  surprisingly  modified  and  improved  by  careful  selection : 
in  peacocks,  from  not  being  very  easily  reared  and  a  large 
stock  not  kejit :  in  geese,  from  being  valuable  only  for  two 
puqioses,  food  and  featliers,  and  more  especially  from  no 
plccisure  having  lieen  felt  in  the  display  of  distinct  breeds  ;  but 
the  goose  seems  to  have  a  singularly  inflexible  organization. 


50  SUMMARY  OF  VAEIATION.  Chap.  I. 

Some  authors  have  maintained  that  the  amount  of  varia- 
tion in  our  domestic  productions  is  soon  reached,  and  can 
never  afterward  be  exceeded.  It  would  be  somewhat  rash  to 
assert  that  the  limit  has  been  attained  in  any  one  case ;  for 
almost  all  our  animals  and  plants  have  been  g'reatly  improved 
in  many  ways  within  a  recent  period ;  and  this  imjilies  varia- 
tion. It  would  be  equally  rash  to  assert  that  characters  now 
increased  to  their  vitmost  limit,  could  not,  after  remaining  fixed 
for  many  centuries,  again  vary  under  new  conditions  of  hfe. 
No  doul)t,  as  Mr.  Wallace  has  remarked  with  much  truth,  a 
limit  will  be  at  last  reached.  For  instance,  there  must  be  a 
limit  to  the  fleetness  of  any  terrestrial  animal,  as  this  will  be 
determined  by  the  friction  to  be  overcome,  the  weight  of  body 
to  be  carried,  and  the  power  of  contraction  in  the  muscular 
fibres.  But  what  concerns  us  is  that  the  domestic  varieties 
of  the  same  species  differ  from  each  other  in  almost  every 
character,  Mhich  man  has  attended  to  and  selected,  more  than 
do  the  distinct  species  of  the  same  genera.  Isidore  Geoffroy 
St.-Hilaire  has  proved  this  in  regard  to  size,  and  so  it  is  with 
color,  and  probably  Muth  the  length  of  hair.  With  respect  to 
fleetness,  which  depends  on  many  bodily  characteristics.  Eclipse 
was  far  fleeter,  and  a  drajMiorse  is  incomparably  stronger,  than 
any  two  equine  species.  So  with  plants,  the  seeds  of  the  dif- 
ferent varieties  of  the  bean  or  maize  difl'cr  more  in  size  than 
do  the  seeds  of  the  distinct  species  in  any  one  genus  of  the 
same  two  families.  The  same  remark  holds  good  in  regard 
to  the  fruit  of  the  several  varieties  c»f  the  plum,  and  still  more 
so  with  the  melon,  as  well  as  in  endless  other  analogous  cases. 

To  sum  up  on  the  origin  of  our  domestic  races  of  animals 
and  plants.  Changed  conditions  of  life  are  of  the  highest  im- 
portance in  causing  variability,  both  directly  l)y  acting  on  the 
organization,  and  indirectly  by  aft'ccting  the  reproductive  sj's- 
tem.  It  is  not  probable  that  variability  is  an  inherent  and 
necessary  contingent,  under  all  circumstances.  The  greater 
or  less  force  of  inheritance  and  reversion  determine  Avhether 
variations  shall  endure.  Yariability  is  governed  by  many  un- 
known laws,  more  especially  by  that  of  correlation.  Some- 
Ihing  may  be  attributed  to  the  definite  action  of  the  conditions 
of  life,  but  how  much,  we  do  not  know.  Something  must  be 
:iltiil)uted  to  use  and  disuse.  The  final  result  is  thus  rendered 
inllnilely  comjilex.  In  some  cases  the  intercrossing  of  abori- 
ginally distinct  species,  has  probably  played  an  important  part 
in  the  orijxin  of  oin*  domestic  breeds.     When  several  breeds 


Chap.  I.  SUMMARY  OF  VAEIATION.  51 

have  once  been  formed  in  any  country,  their  occasional  inter- 
crossing-, -with  the  aid  of  selection,  has,  no  doubt,  largely  aided 
in  forming  new  sub-breeds  ;  but  the  importance  of  crossing 
has  been  much  exaggerated,  both  in  regard  to  animals  and 
to  those  plants  which  are  propagated  by  seed.  With  plants 
which  are  temporarily  propagated  by  cuttings,  buds,  etc,  the 
importance  of  crossing  is  immense  ;  for  the  cultivator  may 
here  disregard  the  extreme  variability  both  of  hybrids  and  of 
mongrels,  and  the  frequent  sterility  of  hybrids ;  but  plants 
not  propagated  by  seed  are  of  little  importance  to  us,  for  their 
endurance  is  only  temporary.  Over  all  these  causes  of  Change 
the  accumulative  action  of  Selection,  whether  applied  method- 
ically and  quickly,  or  unconsciously  and  slowly,  but  more  efB- 
ciently,  is  by  far  the  predominant  Power. 


VAEIATION  UNDER  NATURE.  Chap.  II. 


CHAPTER   II. 

VARIATION   UXDER   NATURE. 

Variability— Individual  Differences— Doubtful  Species— Wide-ranging,  much  dif- 
fused, and  Common  Species,  vary  meet- Species  of  the  Larger  Genera  in  each 
Country  vai"y  more  frequently  than  the  Species  of  the  Smaller  Genera— Many  of 
the  Species  of  the  Larger  Genera  resemble  Varieties  in  being  very  closely,  bat 
unequally,  related  to  each  other,  and  in  having  Restricted  Ranges. 

Before  applying  the  principles  arrived  at  in  the  last  cha|> 
ter  to  organic  beings  in  a  state  of  nature,  we  must  briefly  dis- 
cuss whether  these  latter  are  subject  to  any  variation.  To 
treat  this  subject  at  all  properlj^  a  long  catalogue  of  dry  facts 
ought  to  be  given;  but  these  I  shall  reserve  for  my  future 
work.  Nor  shall  I  here  discuss  the  various  definitions  which 
have  been  given  of  the  term  species.  No  one  definition  has 
as  yet  satisfied  all  naturalists  ;  yet  every  naturalist  knows 
vaguely  what  he  means  when  he  speaks  of  a  species.  Gen- 
erally the  term  includes  the  unknown  element  of  a  distinct 
act  of  creation.  The  term  "variety"  is  almost  equally  difficult 
to  define ;  but  here  community  of  descent  is  almost  universally 
implied,  though  it  can  rarely  be  proved.  We  have  also  what 
are  called  monstrosities ;  but  they  graduate  into  varieties. 
By  a  monstrosity  I  presume  is  meant  some  considerable  devia- 
tion of  structure,  generally  injurious  to  or  not  useful  to  the 
species.  Some  authors  use  the  term  "variation"  in  a  techni- 
cal sense,  as  implying  a  modification  directly  due  to  the  physi- 
cal conditions  of  life ;  and  "  variations  "  in  this  sense  are  sup- 
posed not  to  be  inherited :  but  who  can  say  that  the  dwarfed 
condition  of  shells  in  the  brackish  waters  of  the  Baltic,  or 
dwarfed  plants  on  Alpine  summits,  or  the  thicker  fur  of  an 
animal  from  far  northward,  would  not  in  some  cases  be  inher- 
ited for  at  least  some  few  generations  ?  and  in  this  c;ise  I 
presume  that  the  form  would  be  called  a  variety. 

It  may  be  doubted  whether  sudden  and  great  deviations  of 
structure  such  as  we  occasionally  see  in  our  domestic  produc- 


Chap.  II.  INDIVIDUAL  DIFFERENCES.  53 

tions,  more  especially  with  plants,  are  ever  permanently  prop- 
agated in  a  state  of  nature.  Almost  every  part  of  every 
organic  being  is  so  beautifully  related  in  its  complex  conditions 
of  life  that  it  seems  as  improbable  that  any  part  should  have 
been  suddenly  produced  perfect,  as  that  a  complex  machine 
should  have  been  invente4  by  man  in  a  perfect  state.  Under 
domestication  monstrosities  often  occur  which  resemble  noi 
mal  structures  in  widely-different  animals.  Thus  pigs  have 
often  been  born  with  a  sort  of  proboscis  like  that  of  tlie  tapir 
or  elephant.  Now,  if  any  wild  species  of  the  pig-genus  had 
naturally  possessed  a  proboscis,  it  might  have  been  argued  that 
tliis  in  like  manner  had  suddenly  appeared  as  a  monstrosity  ; 
but  I  have  as  yet  failed  to  find,  after  diligent  search,  cases  of 
monstrosities  resembling  normal  structures  in  nearly-allied 
forms,  and  these  alone  would  bear  on  the  question.  If  mon- 
strous forms  of  this  kind  ever  do  appear  in  a  state  of  nature 
and  are  capable  of  propagation  (which  is  not  always  the  case), 
as  they  occur  rarely  and  singly,  their  preservation  would  de- 
pend on  unusually  favorable  circumstances.  They  would,  also, 
during  the  first  and  succeeding  generations  cross  with  the  or- 
dinary form,  and  thus  they  would  almost  inevitably  lose  their 
abnormal  character.  But  I  shall  have  to  retvu^n  in  a  future 
cliapter  to  the  preservation  and  perpetuation  of  occasional  va- 
riations. 

Individual  Differences. 

Tlie  many  slight  differences  Avhich  frequently  appear  in  the 
offspring  from  the  same  parents,  or  which  may  be  presumed  to 
have  thus  arisen,  from  being  frequently  observed  in  the  indi- 
viduals of  the  same  species  inhabiting  the  same  confined  local- 
ity, may  be  called  indiA-idual  differences.  No  one  supposes 
that  all  the  indi\'iduals  of  the  same  species  are  cast  in  the  same 
actual  mould.  These  individual  differences  are  of  the  highest 
importance  for  us,  for  they  are  often  inherited,  as  must  be  fa- 
miliar to  every  one ;  and  they  thus  afford  materials  for  natural 
selection  to  act  on  and  accumulate,  in  the  same  manner  as  man 
accumulates  in  any  given  direction  individual  differences  in 
his  domesticated  production.s.  These  individual  differences 
generally  affect  what  naturalists  consider  unimportant  parts  ; 
but  I  could  show,  by  a  long  catalogue  of  facts,  that  parts  which 
must  be  called  important,  whether  viewed  under  a  physiolo- 
gical or  classificatory  point  of  view,  sometimes  vary  in  the  indi- 
viduals of  the  same  species.     I  am  convinced  that  the  most  ex- 


54  INDIVIDUAL  DIFFERENCES.  Chap.  II. 

perienced  naturalist  would  be  surprised  at  the  number  of  the 
oases  of  variability,  even  in  important  parts  of  structure,  which 
lie  could  collect  on  ^ood  authority,  as  I  have  collected,  during 
a  course  of  years.  It  should  be  remembered  that  systematists 
are  far  from  bcing^  pleased  at  finding  variability  in  important 
characters,  and  that  there  are  not  many  men  who  wiU  labori- 
ously examine  internal  and  important  ort^ans,  and  compare 
tliem  in  many  specimens  of  the  same  species.  It  Avould  never 
have  been  expected  that  the  branching  of  the  main  nerves  close 
to  the  great  central  ganglion  of  an  insect  would  have  been 
variable  in  the  same  species  ;  it  might  have  been  thought  that 
changes  of  this  nature  could  have  been  effected  only  by  slow 
degrees ;  yet,  recently,  Sir  J.  Lubbock  has  shown  a  degree  of . 
variability  in  these  main  nerves  in  Coccus,  which  ma}'  almost 
be  compared  to  the  irregular  branching  of  the  stem  of  a  tree. 
This  philosophical  naturalist,  I  may  add,  has  also  recently 
sliowu  that  the  muscles  in  the  larva?  of  certain  insects  are  far 
from  luiiform.  Authors  sometimes  argue  in  a  circle  when  they 
state  that  important  organs  never  vary  ;  for  these  same  authors 
practically  rank  those  parts  as  important  (as  some  few  natu- 
ralists have  honestly  confessed),  which  do  not  vary  ;  and,  under 
this  point  of  view,  no  instance  will  ever  be  found  of  an  impor- 
tant part  varying :  but  under  any  other  point  of  view  many 
instances  assuredly  can  be  given. 

There  is  one  point  connected  with  individual  differences, 
which  is  extremely  perplexing  :  I  refer  to  those  genera  which 
have  been  called  "  protean  "  or  "  polymorphic,"  in  which  the 
species  present  an  inordinate  amount  of  variation  ;  and  about 
which  hardly  two  naturalists  agree  whether  to  rank  them  as 
species  or  as  varieties.  We  niay  instance  Rubus,  Rosa,  and 
Hieracium  among  plants,  several  genera  of  insects,  several  gen- 
era of  Brachiopod  shells,  and  the  Ruff  (Machetes  pugnax) 
among  birds.  In  most  polpnorphic  genera  some  of  the  species 
have  fixed  and  definite  characters.  Genera  which  are  poly- 
morpliic  in  one  country  seem  to  be,  with  some  few  exceptions, 
])olymorphic  in  other  countries,  and  likewise,  judging  from 
Brachiopod  shells,  at  former  periods  of  time.  These  facts  are 
very  perplexing,  for  they  seem  to  sliow  that  this  kind  of  varia- 
bility is  independent  of  the  conditions  of  life.  I  am  inclined 
to  suspect  that  we  have,  at  least  in  some  of  these  polymorphic 
gen(»ra,  variations  which  are  of  no  service  or  disservice  to  the 
Hpccics,  and  which,  consequently,  have  not  been  seized  on  and 
reiiden^d  delinite  by  natural  selection,  as  hereafter  to  be  ex- 
j)hiined. 


CiiAP.  II.  INDIVIDUAL  DIFFERENCES.  55 

Individuals  of  the  same  species  often  present  ^cat  difTcr- 
eiices  of  structure,  as  in  the  two  sexes  of  various  animals,  iuthe 
two  or  three  castes  of  sterile  females  or  workers  amon^^  insects, 
and  in  the  immature  and  larval  states  of  many  of  the  lower  ani- 
mals. Tlierc  are,  however,  other  cases,  namely,  of  dimori)hism 
and  trimorphism,  which  might  easily  be,  and  have  frecjucntly 
l)een,  confounded  with  varial^ility,  but  which  are  quite  distinct. 
I  refer  to  the  two  or  three  dillerent  forms  which  certain  animals 
of  either  sex,  and  certain  hermaphrodite  plants,  habitually  pre- 
sent. Thus,  Mr.  Wallace,  who  has  lately  called  special  atten- 
tion to  the  subject,  has  shown  that  the  females  of  certain  spe- 
cies of  butterflies,  in  the  Malayan  archipelaj^o,  regularly  ap- 
pear under  two  or  even  three  consjoicuously  distinct  forms,  not 
connected  together  by  intermediate  varieties.  The  winged  and 
frequently  wingless  states  of  so  many  Hemipterous  insects  may 
probably  be  included  as  a  case  of  dimorphism,  and  not  of  mere 
variability.  Fritz  Muller,  also,  has  recently  described  analo- 
gous but  more  extraordinary  cases  with  the  males  of  certain 
Brazilian  Crustaceans  :  thus,  the  male  of  a  Tanais  regularly 
occurs  under  two  widely-dillerent  forms,  not  connected  by  any 
intermediate  links ;  one  of  these  forms  has  much  stronger  and 
differently-shaped  pincers  for  seizing  the  female,  and  the  other, 
as  if  for  compensation,  has  anlennaj  much  more  abundantly 
furnished  with  smelhng-hairs,  so  as  to  have  a  better  chance  of 
finding  the  female.  Again,  the  males  of  another  Crustacean, 
an  Orchestia,  occur  under  two  distinct  forms,  with  pincers  dif- 
fering much  more  from  each  other  in  structure,  than  do  the 
pincers  of  most  species  of  the  same  genus.  With  respect  to 
plants,  I  have  recently  shown  that  in  several  -widely-distinct 
orders,  the  species  present  two  or  even  three  forms,  which  arc 
abruptly  distinguished  from  each  other  in  several  important 
]ioints,  as  in  the  size  and  color  of  the  pollen-grains  ;  and  these 
forms,  though  all  hermaphrotlites,  differ  from  each  other  in 
their  reproductive  power,  so  that  for  full  fertility,  or  indeed  in 
some  cases  for  any  fertility,  they  must  reciprocally  impregnate 
each  other.  Although  the  forms  of  the  few  dimorphic  and  tri- 
morphic  animals  and  plants  which  have  been  studied,  are  not 
now  connected  together  by  intermi^diate  links,  it  is  ]irol)able 
that  thi^  will  be  found  to  occur  in  other  cases  ;  for  Mr.  \\''allacc 
observed  a  certain  Ijutterlly  which  jiresentcd  in  the  same  island 
a  great  range  of  varieties  connected  by  intermediate  links,  and 
the  extreme  links  of  the  chain  closely  resembled  the  two  forms 
of  an  allied  dimorphic  species  inhabiting  another  part  of  the 


5G  DOUBTFUL  SPECIES.  CnAP.  II, 

Malay  archipelago.  Tlius  also  with  ants,  the  several  worker- 
castes  are  generally  cjuite  distinct ;  but  in  some  cases,  as  we 
shall  hereafter  see,  the  castes  are  connected  together  by  gradu- 
ated varieties.  It  certainly  at  first  appears  a  highly-remark- 
able fact  that  the  same  female  butterfly  should  have  the  power 
of  producing  at  the  same  time  three  distinct  female  forms  and 
a  male  ;  that  a  male  Crustacean  should  generate  two  male 
forms  and  a  female  form,  all  widely  different  from  each  other ; 
and  that  an  hermaphrodite  plant  should  produce  from  the  same 
seed-capsule  three  distinct  hermaplu-odite  forms,  bearing  three 
different  kinds  of  females  and  three  or  even  six  different  kinds 
of  males.  Nevertheless  these  cases  are  only  exaggerations  of 
the  universal  fact  that  every  female  produces  males  and  females, 
Avhich  in  some  instances  differ  in  a  wonderful  manner  fj-omeach 
other. 

Doubtful  jSpecies. 

The  forms  which  possess  in  some  considerable  degree  the 
character  of  species,  but  which  are  so  closely  similar  to  other 
forms,  or  are  so  closely  linked  to  them  by  intermediate  grada- 
tions, that  naturalists  do  not  like  to  rank  them  as  distinct 
species,  are  in  several  respects  the  most  important  for  us.  We 
have  every  reason  to  believe  that  many  of  these  doubtful  and 
closely-allied  forms  have  permanently  retained  their  characters 
in  their  own  country  for  a  long  time ;  for  as  long,  as  far  as  we 
knoAV,  as  have  good  and  true  species.  Practically,  when  a 
naturalist  can  unite  two  forms  together  by  othei*s  having  inter- 
mediate characters,  he  treats  the  one  as  a  variety  of  the  other, 
ranking  the  most  common,  but  sometimes  the  one  first  de- 
scribed, as  the  species,  and  the  other  as  the  variety.  But 
cases  of  great  difliculty,  which  I  will  not  here  enumerate, 
sometimes  occur  in  deciding  whether  or  not  to  rank  one  form 
as  a  variety  of  another,  even  when  they  are  closely  connected 
by  intermediate  links  ;  nor  will  the  commonly-assumed  hybrid 
nature  of  the  intermediate  links  always  remove  the  difficulty. 
In  very  many  cases,  however,  one  form  is  ranked  as  a  variety 
of  another,  not  because  the  intermediate  links  have  actually 
been  found,  but  because  analogy  leads  the  observer  to  suppose 
either  that  they  do  now  somewhere  exist,  or  may  formerly 
have  existed  ;  and  here  a  wide  door  for  tlie  entry  of  doubt  and 
conjecture  is  opened. 

Hence,  in  determining  whether  a  form  should  be  ranked  as 
a  species  or  a  variety,  the  opinion  of  naturalists  having  sound 


Chap.  II.  DOUBTFUL  SPECIES.  57 

judgment  and  wide  experience  seems  the  only  guide  to  follow. 
itVe  must,  however,  in  many  cases,  decide  by  a  majority  of 
naturalists,  for  few  well-marked  and  well-known  varieties  can 
be  named  which  have  not  been  ranked  as  species  by  at  least 
some  competent  judges. 

That  varieties  of  this  doubtful  nature  are  far  from  uncom- 
mon cannot  be  disputed.  Compare  the  several  floras  of  Great 
Britain,  of  France,  or  of  the  United  States,  drawn  up  by  dif- 
ferent botanists,  and  see  Avhat  a  surprising  number  of  forms 
have  been  ranked  by  one  botanist  as  good  species,  and  by  an- 
other as  mere  varieties.  ^Ir.  H.  C.  Watson,  to  whom  I  lie 
inider  deep  obligation  for  assistance  of  all  kinds,  has  marked 
fur  me  18"v  British  plants,  which  are  generally  considered  as 
varieties,  but  which  have  all  been  ranked  by  botanists  as  spe- 
cies ;  and  in  making  this  list  he  has  omitted  many  trifling  varie- 
ties, but  which  nevertheless  have  been  ranked  by  some  bota- 
nists as  specie's,  and  he  has  entirely  omitted  several  bighly-poly- 
morj^hic  genera.  Under  genera,  including  the  most  polymor- 
{)hic  forms,  Mr.  Babington  gives  251  species,  whereas  Mr. 
Benthara  gives  only  112 — a  difference  of  139  doubtful  forms  ! 
Among  animals  which  unite  for  each  birth,  and  which  are 
highly  locomotive,  doubtful  forms,  ranked  by  one  zoologist  as 
a  species  and  by  another  as  a  variety,  can  rarely  be  found 
within  the  same  country,  but  are  common  in  separated  areas. 
How  many  of  those  birds  and  insects  in  North  America  and 
Europe,  which  differ  very  slightly  from  each  other,  have  been 
ranked  by  one  eminent  naturalist  as  undoubted  species,  and  by 
another  as  varieties,  or,  as  they  are  often  called,  as  geographical 
races  !  Mr.  Wallace,  in  several  valuable  papers  on  the  various 
animals,  especially  on  the  Lepidoptera,  inhabiting  the  islands  of 
the  great  Malayan  archipelago,  shows  that  they  may  be  classed 
under  four  heads,  namely,  as  variable  forms,  as  local  forms, 
as  geographical  races  or  sul)-species,  and  as  true  representative 
species.  The  first  or  variable  forms  vary  much  within  the 
limits  of  the  same  island.  The  local  forms  are  moderately 
constant  and  distinct  in  eqch  separate  island;  but  when  all 
the  forms  from  the  several  islands  arc  compared,  the  differ- 
ences are  seen  to  be  so  slight  and  graduated,  that  it  is  impos- 
sible to  define  or  describe  them,  though  at  the  same  time  the 
extreme  forms  are  sufficiently  distinct.  The  geographical 
races  or  sul>speoies  are  local  forms  completely  fixed  and  iso- 
lated; but  as  they  do  not  differ  from  each  other  by  strongly- 
marked  and  important  characters, "  there  is  no  possible  test  but 


58  DOUBTFUL  SPECIES.  Cuap.  II. 

individual  opinion  to  determine  which  of  them  shall  be  consid- 
ered as  species  and  -which  as  varieties."  Lastly,  representa- 
tive species  fill  the  same  place  in  the  natural  economy  of  each 
island  as  do  the  local  forms  and  sub-species  ;  but,  as  they  are 
distinp^uished  from  each  other  by  a  greater  amount  of  differ- 
ence than  that  between  the  local  forms  and  sub-species,  they 
are  almost  imiversally  ranked  by  naturalists  as  true  species. 
Nevertheless,  no  certain  criterion  can  possibly  be  given  by 
which  variable  forms,  local  forms,  sub-species,  and  representa- 
tive species  can  be  recognized. 

Many  years  ago,  when  comparing,  and  seeing  others  com- 
pare, the  birds  from  the  closely-neighboring  islands  of  the 
Galapagos  archipelago,  both  one  with  another,  and  with  those 
from  the  American  main-land,  I  was  much  struck  how  entirely 
vague  and  arbitrary  is  the  distinction  between  species  and 
varieties.  On  the  islets  of  the  little  Madeira  group  there  are 
many  insects  Avhich  are  characterized  as  varieties  in  Mr.  Wol- 
laston's  admirable  work,  but  which  would  certainly  be  ranked 
as  distinct  species  by  many  entomologists.  Even  Ireland  has 
a  few  animals,  now  generally  regarded  as  varieties,  but  which 
have  been  ranked  as  species  by  some  zoologists.  Several 
experienced  ornithologists  consider  our  British  red  grouse  as 
only  a  strongly-marked  race  of  a  Norwegian  species,  whereas 
the  greater  number  rank  it  as  an  undoubted  species  peculiar 
to  Great  Britain.  A  wide  distance  between  the  homes  of  two 
doubtful  forms  leads  many  naturalists  to  rank  them  as  distinct 
species  ;  but  what  distance,  it  has  been  Avell  asked,  Avill  suf- 
fice ;  if  that  between  America  and  Europe  is  ample,  will  that 
lietween  Europe  and  the  Azores,  or  Madeira,  or  tlie  Canaries, 
or  between  the  several  islets  of  these  small  archipelagos,  be 
sufficient  ? 

Mr.  B.  D.  Walsh,  a  distinguished  entomologist  of  the  United 
States,  has  lately  described  what  he  calls  Phytophagic  varieties 
and  Phytophagic  species.  Most  vegetable-feeding  insects  live 
on  one  kind  of  plant  or  on  one  group  of  plants  ;  some  feed  in- 
discriminately on  many  kinds,  but  do  not  in  consequence  vary. 
In  several  cases,  however,  insects  found  living  on  different 
plants  have  been  observed  by  Mr.  Walsh  to  present,  either  ex- 
el  usivel}'  in  their  larval  or  mature  state,  or  in  both  states, 
slight  though  constant  differences  in  color,  size,  or  in  the  nature 
of  their  secretions.  In  some  instances  the  males  alone,  in  other 
instances  l)()th  males  and  females,  liave  been  olisen'ed  to  be 
thus  alTected  in  a  shght  degree.      When  the  diflerencos  are 


Chap.  II.  DOUBTFUL  SPECIES.  59 

rather  more  strongly  marked,  and  when  both  sexes  and  all  aj^os 
are  afTectcd,  the  forms  -would  be  ranked  by  all  entomolo<^ists  as 
species.  But  no  observer  can  determine  for  others,  even  if  he 
can  do  so  for  himself,  which  of  these  Phytophagic  forms  ought 
to  be  called  species  and  which  varieties.  Mr.  Walsh  ranks  the 
forms  which  it  may  be  supposed  would  freely  intercross  together, 
as  varieties ;  and  those  Avhich  appear  to  have  lost  this  jjower, 
as  species.  As  the  ditfcrences  depend  on  the  insects  having 
long  fed  on  distinct  plants,  it  cannot  be  expected  that  inter- 
mediate links  connecting  tlie  several  forms  should  now  be 
found.  The  naturalist  thus  loses  his  best  guide  in  determining 
whether  to  rank  such  doubtful  forms  as  varieties  or  sjiecies. 
This  likewise  necessarily  occurs  with  closely-allied  organisms, 
which  inhabit  distinct  continents  or  islands.  When,  on  the 
other  hand,  an  animal  or  plant  ranges  over  the  same  continent, 
or  inhabits  many  islands  in  the  same  archipelago,  and  presents 
different  forms  in  the  different  areas,  there  is  always  a  good 
chance  that  intermediate  forms  may  be  discovered  which  shall 
link  together  the  extreme  states ;  and  these  arc  then  degraded 
to  the  rank  of  varieties. 

Some  few  naturalists  maintain  that  animals  never  present 
varieties ;  but  then  these  same;  naturalists  rank  the  slightest 
differences  as  of  specific  value;  and  when  the  same  identical 
form  is  met  with  in  two  distant  countries,  or  in  tM'o  geological 
formations,  they  believe  that  two  distinct  species  are  hidden 
under  the  same  dress.  Tlie  term  species  thus  comes  to  be  a 
mere  useless  mental  abstraction,  implying  and  assuming  a  sepa 
rate  act  of  creation.  It  is  certain  that  many  forms,  considered 
by  highly-competent  judges  as  varieties,  so  completely  resemble 
species  in  character,  that  they  have  been  thus  ranked  by  other 
highly-competent  judges.  But  to  discuss  whether  they  ought 
to  lie  called  species  or  varieties,  before  any  definition  of  these 
terms  has  been  generally  accepted,  is  A'ainly  to  beat  the  air. 

Many  of  the  cases  of  strongly-marked  varieties  or  doul)tful 
species  well  deserve  consideration  ;  for  several  interesting  lines 
of  argument,  from  geographical  distribution,  analogical  varia- 
tion, hybridism,  etc.,  have  been  brought  to  l)ear  on  tlie  attempt 
to  determine  their  rank  ;  but  space  does  not  here  permit  me 
to  discuss  them.  Close  investigation,  in  many  cases,  will  bring 
naturalists  to  an  agreement  how  to  rank  doubtfid  forms.  Yet 
it  must  be  confessed  that  it  is  in  the  best-known  countries  that 
we  find  the  greatest  number  of  forms  of  doubtful  value.  I 
have  been  struck  Avith  the  fact  that,  if  any  animal  or  plant  in  a 


CO  DOUBTFUL  SPECIES.  Chap.  II. 

state  of  nature  be  liigbly  useful  to  man,  or  from  any  cause 
closely  attract  his  attention,  varieties  of  it  will  almost  univer- 
sally be  found  recorded.  These  varieties,  moreover,  will  often 
be  ranked  by  some  authors  as  species.  Look  at  the  common 
oak,  how  closely  it  has  been  studied;  yet  a  German  author 
makes  more  than  a  dozen  species  out  of  forms,  which  are  almost 
imiversally  considered  as  varieties ;  and  in  this  country  the 
highest  botanical  authorities  and  practical  men  can  Ix)  quoted 
to  show  that  the  sessile  and  pedunculated  oaks  are  either  good 
and  distinct  species  or  mere  varieties. 

I  may  here  allude  to  a  remarkable  memoir  lately  published 
by  A.  de  Candolle,  on  the  oaks  of  the  whole  world.  No  one 
ever  had  more  ample  materials  for  the  discrimination  of  the 
species,  or  could  have  worked  on  them  with  more  zeal  and 
sagacity.  He  first  gives  in  detail  all  the  many  points  of  struc- 
ture which  vary  in  the  species,  and  estimates  numerically  the 
relative  frequency  of  the  variations.  He  specifics  above  a 
dozen  characters  Avliich  niay  be  found  varying  even  on  the  same 
branch,  sometimes  according  to  age  or  development,  sometimes 
without  any  assignable  reason.  Such  characters  of  course  are 
not  of  specific  value,  but  they  are,  as  Asa  Gray  has  remarked 
in  commenting  on  this  memoir,  such  as  generally  enter  into 
specific  definitions.  De  Candolle  then  goes  on  to  saj^-  that  he 
gives  the  rank  of  species  to  the  forms  that  differ  by  characters 
never  varying  on  the  same  tree,  and  never  found  connected  by 
intermediate  states.  After  this  discussion,  the  result  of  so 
much  labor,  he  emphatically  remarks  :  "  They  are  mistaken, 
who  repeat  that  the  greater  part  of  our  species  arc  clearly 
limited,  and  that  the  doubtful  species  are  in  a  feeble  minority. 
This  seemed  to  be  true,  so  long  as  a  genus  was  imperfectly 
known,  and  its  species  Avere  fovuidcd  upon  a  few  specimens, 
that  is  to  say,  were  provisional.  Just  as  we  come  to  know 
them  better,  intermediate  forms  flow  in,  and  doubts  as  to  spe- 
cific limits  augment."  He  also  adds  that  it  is  the  best-known 
species  which  present  the  greatest  number  of  spontaneous 
varieties  and  sub-varieties.  Thus.Quercus  robur  has  twenty- 
eight  varieties,  all  of  which,  excepting  six,  are  clustered  round 
three  sub-species,  namely,  Q.  peduuculata,  sessilifiora,  and 
pubescens.  The  forms  which  connect  these  three  sulvspecies 
are  comparatively  rare ;  and,  as  Asa  Gray  remarks,  if  these 
connecting  forms,  whi(;h  are  now  rare,  were  to  become  wholly 
extinct,  the  three  sub-species  Avould  hold  exactly  the  same 
relation  to  each  other,  as  do  the  four  or  five  provisionally- 


Cnxr.  II.  DOUBTFUL  SPECIES.  61 

admitted  species  which  closely  surround  the  typical  Qucnuis 
rol)ur.  Finally,  De  Candolle  admits  that,  out  of  the  three  hun- 
dred species,  Avhicli  will  l^e  enumerated  in  his  Prodromus  as 
belonging  to  the  oak  family,  at  least  two-thirds  are  provisional 
species,  that  is,  are  not  known  strictly  to  fulfil  the  definition 
above  given  of  a  true  species.  For  it  should  be  added  that  De 
Candolle  no  longer  believes  that  species  are  immutable  crea- 
tions, but  concludes  that  the  derivative  theory  of  the  succession 
of  forms  is  the  most  natural  one,  "  and  the  most  accordant  with 
tlie  known  facts  in  paleontology,  geographical  botany  and  zo- 
ology, of  anatomical  structure  and  classification  ; "  but,  he  adds, 
direct  proof  is  still  wanting. 

When  a  young  naturalist  commences  the  study  of  a  group 
of  organisms  quite  unknown  to  him,  he  is  at  first  much  per- 
plexed to  determine  what  difiercnces  to  consider  as  specific,  and 
what  as  varietal ;  for  he  knows  nothing  of  the  amount  and 
kind  of  variation  to  which  the  group  is  subject ;  and  this  shows, 
at  least,  how  very  generally  there  is  some  variation.  But  if  he 
confine  his  attention  to  one  class  within  one  country,  he  will 
soon  make  up  his  mind  how  to  rank  most  of  the  doubtful  forms. 
His  general  tendency  will  be  to  make  many  species,  for  he  will 
become  impressed,  just  like  the  pigeon  or  poultry  fancier  l)eforc 
alluded  to,  with  the  amount  of  difference  in  the  forms  which  he 
is  continually  studying ;  and  he  has  little  general  knowledge 
of  analogical  variation  in  other  groups  and  in  other  countries, 
by  which  to  corrett  his  first  impressions.  As  he  extends  the 
range  of  his  oljservations,  he  will  meet  Avith  more  cases  of  diffi- 
culty ;  for  ho  will  encounter  a  greater  number  of  closely-allied 
forms.  But  if  his  observations  be  widely  extended,  he  will  in 
the  end  generally  l)e  enaljled  to  make  up  his  own  mind  which 
to  call  varieties  and  wliich  species  ;  but  he  will  succeed  in  this 
at  the  expense  of  admitting  much  variation — and  the  truth  of 
this  admission  will  often  be  disputed  by  other  naturalists. 
AV'hen,  moreover,  he  comes  to  study  allied  forms  brought  from 
countries  not  now  continuous,  in  which  case  he  cannot  hope  to 
find  tlie  intermediate  links  between  his  doubtful  forms,  he  will 
have  to  trust  almost  entirely  to  analog}-,  and  his  difliculties  rise 
to  a  climax. 

Certainl}^  no  clear  line  of  demarcation  has  as  yet  been  drawn 
between  species  and  sub-sju^cies — that  is,  the  forms  which  in 
the  ojjinion  of  some  naturalists  come  very  near  to,  but  do  not 
quite  arrive  at,  the  rank  of  species:  or,  again,  between  sub- 
species and  well-marked  varieties,  or  between  lesser  varieties  and 


G2  DOMINANT  SPECIES  VARY  MOST.  Chap.  II. 

individual  differences.  These  differences  blend  into  each  other 
in  an  insensible  scries ;  and  a  seiies  impresses  the  mind  with 
the  idea  of  an  actual  passage. 

Hence,  I  look  at  individual  differences,  though  of  small 
interest  to  the  systematist,  as  of  the  highest  importance  for 
us,  as  being  the  first  steps  toward  such  slight  varieties  as  are 
barely  thought  worth  recording  in  works  on  natural  history. 
And  I  look  at  varieties  which  are  in  any  degree  more  distinct 
and  permanent,  as  steps  toward  more  strongly-marked  and 
permanent  varieties  ;  and  at  the  latter,  as  leading  to  sub- 
species or  species.  The  passages  from  one  stage  of  difference 
to  another  may,  in  some  cases,  be  the  simple  result  of  the 
long-continued  action  of  different  physical  conditions ;  but  in 
most  cases  they  may  be  attributed  to  the  gradual  accumulative 
'action  of  natural  selection,  as  hereafter  to  be  more  fullj"  ex- 
plained, on  fluctuating  variability.  •  Hence  a  well-marked 
variety  may  be  called  an  incipient  species  ;  but  whether  this 
belief  is  justifiable  must  be  judged  of  by  the  general  weight 
of  the  facts  and  considerations  given  throughout  this  Avork. 

It  need  not  be  supposed  that  all  varieties  or  incipient  spe- 
cies necessarily  attain  the  rank  of  species.  They  may  become 
extinct,  or  they  may  endure  as  varieties  for  very  long  periods, 
as  has  been  shown  to  be  the  case  by  Mr.  Wollaston  with  the 
varieties  of  certain  fossil  land-shells  in  Madeira,  and  with  plants 
by  Gaston  de  Saporta,  If  a  variety  were  to  flourish  so  as  to 
exceed  in  immbers  the  parent-species,  it  would  then  rank  as 
the  species,  and  the  species  as  the  variety ;  or  it  might  come 
1o  supplant  and  exterminate  the  parent-species  ;  or  both  might 
coexist,  and  both  rank  as  independent  species.  But  we  shall 
hereafter  return  to  this  subject. 

From  these  remarks  it  will  be  seen  that  I  look  at  the  term 
species  as  one  arbitrarily  given,  for  tlie  sake  of  convenience, 
to  a  set  of  individuals  closely  resembling  each  other,  and  that 
it  does  not  essentially  differ  from  the  term  variety,  which  is 
given  to  less  distinct  and  more  fluctuating  forms.  The  term 
variety,  again,  in  comparison  with  mere  individual  differences, 
is  also  applied  arbitrarily,  and  for  mere  convenience'  sake. 

Wide-ranging^  much-d {fused,  and  Commo7i  Siyecics,  vary 

most. 

Guided  by  theoretical  considerations,  I  thought  that  some 
interesting  results  might  be  obtained  in  regard  to  the  nature 


Chat.  II.  DOMINANT  SPECIES  VARY  MOST.  63 

and  relations  of  the  species  which  vary  most,  by  tabulatinj^ 
all  the  varieties  in  several  Avell-workcd  floras.  At  first  this 
seemed  a  simple  task ;  but  Mr.  H.  C.  W^atson,  to  whom  I  am 
much  indebted  for  valuable  advice  and  assistance  on  this  sub- 
ject, soon  convinced  me  that  there  were  many  difficulties,  as 
did  subsequently  Dr.  Hooker,  even  in  strono^er  terms.  I  shall 
reserve  •  for  my  future  work  the  discussion  of  these  difficulties, 
and  the  tables  themselves  of  the  proportional  numbers  of  the 
varying  species.  Dr.  Hooker  permits  me  to  add  that,  after 
liaviufT'  carefully  read  my  manuscript,  and  examined  the  tables, 
he  tliinks  tliat  the  follo\\ing  statements  are  fairly  well  estab- 
lished. The  whole  subject,  however,  treated  as  it  necessarily 
here  is  with  much  brevity,  is  rather  pcrplexin;T,  and  allusions 
cannot  be  avoided  to  the  "struggle  for  existence,"  "divergence 
of  character,"  and  other  cjuestions,  hereafter  to  be  discussed. 

Alphonse  de  Candollc  and  others  have  shown  that  plants 
which  have  very  wide  ranges  generally  present  varieties  ;  and 
this  might  have  been  expected,  as  they  become  exposed  to 
diverse  physical  conditions,  and  as  they  come  into  competition 
(which,  as  we  shall  hereafter  see,  is  an  equally  or  more  im- 
portant circumstance,  with  different  sets  of  organic  beings.  But 
my  ta])les  further  show  that,  in  any  limited  country,  the  species 
winch  arc  most  common,  that  is,  abound  most  in  individuals, 
and  the  species  Avhich  are  most  widely  diifused  within  their 
own  country  (and  this  is  a  different  consideration  from  wide 
range,  and  to  a  certain  extent  from  commonness)  oftenest  give 
rise  to  varieties  sufficiently  well  marked  to  have  been  recorded 
in  botanical  works.  Hence  it  is  the  most  flourishing,  or,  as 
they  may  be  called  the  dominant  species — those  which  range 
widely,  are  the  most  diffused  in  their  own  country,  and  arc  the 
most  numerous  in  individuals — wln'ch  oftenest  produce  well- 
marked  varieties,  or,  as  I  consider  them,  incipient  species. 
And  this,  perhaps,  might  have  been  anticipated;  for,  as  varie- 
ties, in  order  to  become  in  any  degree  permanent,  necessarily 
have  to  struggle  with  the  other  inhabitants  of  the  coimtry, 
the  species  which  are  already  dominant  will  be  the  most  likely 
to  yield  olTspring,  which,  though  in  some  slight  degree  modi- 
fied, still  inlu^rit  those  advantages  tliat  enabled  their  parents  to 
become  dominant  over  their  compatriots.  In  these  remai'ks 
on  predominance,  it  should  l)e  understood  that  reference  is 
marie  only  to  those  forms  which  come  into  competition  Avith 
each  other,  and  more  especially  to  the  members  of  the  same 
genus  or  class  having  nearly  similar  habits  of  life.     With  re- 


64  SPECIES  OF  LARGER  GENERA  VARIABLE.       Chap.  II. 

spect  to  cominoiinoss  or  the  number  of  individuals  of  any  spe- 
cies, the  comparison,  of  course,  relates  only  to  the  members  of 
the  same  group.  A  plant  may  be  said  to  be  dominant  if  it 
be  more  numerous  in  individuals  and  more  widely  diffused  than 
the  other  plants  of  the  same  country,  not  livini^^  under  widely- 
different  conditions  of  Hfe.  Such  a  plant  is  not  the  less  domi- 
nant in  the  sense  here  used,  because  some  conferva  inhabiting 
the  water  or  some  parasitic  fungus  is  infinitely  more  numerous 
in  individuals,  and  more  widely  diffused  ;  if  one  kind  of  conferva 
or  parasitic  fungus  exceeded  its  allies  in  the  above  respects, 
it  would  be  a  dominant  form  within  its  own  class. 

JSjjecies  of  the  Larger  Genera  in  each  Country  vary  more 
frequently  than  the  Species  of  the  Smaller  Genera. 

If  the  plants  inhabiting  a  country  and  descrilicd  in  any 
Flora  be  divided  into  two  ecjual  masses,  all  those  in  the  larger 
genera  (i.  e.,  those  including  many  species)  being  placed  on 
one  side,  and  all  those  in  the  smaller  genera  on  the  other  side, 
a  somewhat  larger  number  of  the  very  common  and  much-dif- 
fused or  dominant  species  will  be  found  on  the  side  of  the 
larger  genera.  This,  again,  might  have  been  anticipated  ;  for 
the  mere  fact  of  many  species  of  the  same  genus  inhabiting  any 
country,  shows  that  there  is  something  in  the  organic  or  inor- 
ganic conditions  of  that  country  favorable  to  the  genus  ;  and, 
consequently,  we  might  have  expected  to  have  found  in  the 
larger  genera,  or  those  including  many  species,  a  large  propor- 
tional number  of  dominant  species.  But  so  many  causes  tend 
to  obscure  this  result,  that  I  am  surprised  that  my  tables  show 
even  a  small  majority  on  the  side  of  the  larger  genera.  I  will 
here  allude  to  only  two  causes  of  obscurity.  Fresh-water  and 
salt-loving  plants  have  generally  very  wide  ranges  and  are 
much  diffused,  but  this  seems  to  be  connected  with  the  nature 
of  the  stations  inhabited  by  them,  and  has  little  or  no  relation 
to  the  size  of  the  genera  to  which  the  species  belong.  Again, 
plants  low  in  the  scale  of  organization  are  generally  much 
more  widely  diffused  than  plants  higher  in  the  scale ;  and  here, 
again,  there  is  no  close  relation  to  the  size  of  the  genera.  Tlie 
cause  of  lowly-organized  plants  ranging  widely  will  be  discussed 
in  our  chapter  on  Geographical  Distribution. 

From  looking  at  species  as  only  strongly-marked  and  well- 
defined  varieties,  I  was  led  to  anticipate  tliat  the  species  of  the 
larger  genera  in  each  country  would  oftener  present  varieties, 


CnAP.  11.       SPECIES  OF  LARGER  GENERA  VARIABLE.  65 

than  the  species  of  the  smaller  g'enera ;  for  wherever  many 
closely-related  species  (i.  e.,  species  of  the  same  genus)  have 
been  fornietl,  many  varieties  or  incipient  species  ought,  as  a 
general  rule,  to  be  now  forming.  Where  many  large  trees 
grow,  we  expect  to  find  saplings.  Where  many  species  of  a 
genus  have  been  formed  tkrough  variation,  circumstances  have 
been  favorable  for  variation  ;  and  hence  we  might  expect  thai 
the  circumstances  would  generally  be  still  favorable  to  varia- 
tion. On  the  other  hand,  if  we  look  at  each  species  as  a  special 
act  of  creation,  there  is  no  apparent  reason  why  more  varieties 
should  occur  in  a  group  having  many  species,  than  in  one 
having  few. 

To  test  the  truth  of  this  anticipation,  I  have  arranged  the 
j^lants  of  twelve  countries,  and  the  coleopterous  insects  of  two 
districts,  into  two  nearly  equal  masses,  the  species  of  the 
larger  genera  on  one  side,  and  those  of  the  smaller  gCnera  on 
the  other  sid(?,  and  it  has  invariably  proved  to  be  the  case  that 
a  larger  proportion  of  ±he  species  on  the  side  of  the  larger 
genera  presented  varieties,  than  on  the  side  of  the  smaller 
genera.  Moreover,  the  species  of  the  large  genera  which  pre- 
sent any  varieties,  invariably  present  a  larger  average  number 
of  varieties  than  do  the  species  of  the  small  genera.  Both  these 
results  follow  when  another  diWsion  is  made,  and  when  all  the 
least  genera,  with  from  only  one  to  four  species,  are  absolutely 
excluded  from  the  tables.  These  facts  are  of  plain  significa- 
tion on  the  view  that  species  are  only  strongly-marked  and 
permanent  varieties ;  for  wherever  many  species  of  the  same 
genus  have  been  formed,  or  where,  if  we  may  use  the  expres- 
sion, the  manufactory  of  species  has  been  active,  we  ought 
generally  to  find  the  manufactory  still  in  action,  more  espe- 
cially as  we  have  every  reason  to  believe  the  process  of  manu- 
facluring  new  species  to  be  a  slow  one.  And  this  certainly 
is  the  case,  if  varieties  be  looked  at  as  incipient  species ;  for 
my  tables  clearly  show  as  a  general  rule  that,  wherever  many 
speci(^s  of  a  genus  have  been  formed,  the  species  of  that  genus 
present  a  nvunber  of  varieties,  that  is,  of  incipient  species,  be- 
yond the  average.  It  is  not  that  all  large  genera  are  now 
varying  nuich,  and  are  thus  increasing  in  the  lunnber  of  their 
species,  or  that  no  small  genera  are  now  varying  and  increas- 
ing; for  if  this  had  l)een  so,  it  would  have  been  fatal  to  my 
theory  ;  inasmuch  as  geology  plainly  tells  us  that  small  genera 
have  in  the  lapse  of  time  often  increased  greatly  in  size;  and 
that  large  genera  have  often  come  to  their  maxima,  declined, 


OG  SPECIES   OF  LARGER  GENERA  Chap.  II. 

aiul  disappeared.  All  that  we  -want  to  show  is,  that,  where 
many  species  of  a  genus  have  been  formed,  on  an  average 
many  arc  still  forming ;  and  this  certainly  holds  good. 

Many  of  tJic  Sjiccies  included  iclthln  the  Larger  Genera  re- 
semble Varieties  in  being  very  closely,  but  unequally,  related 
to  each  other,  and  in  having  liestricted  Manges. 

There  are  other  relations  between  the  species  of  large  gen- 
era and  their  recorded  varieties  which  deserve  notice.  We 
have  seen  that  there  is  no  infallible  criterion  by  which  to  dis- 
tinguish species  and  well-marked  varieties  ;  and  in  those  cases 
in  which  intermediate  links  have  not  been  found  between 
doubtful  forms,  naturalists  are  compelled  to  come  to  a  deter- 
mination by  the  amount  of  difference  between  them,  judging  by 
analogy  whether  or  not  the  amoimt  suffices  to  raise  one  or  both 
to  the  rank  of  species.  Hence  the  amount  of  difference  is  one 
very  important  criterion  in  settling  whether  two  forms  should  be 
ranked  as  species  or  varieties.  Now  Fries  has  remarked  in 
regard  to  plants,  and  Westwood  in  regard  to  insects,  that  in 
large  genera  the  amount  of  difference  between  the  sjiecies  is 
often  exceedingly  small.  I  have  endeavored  to  test  this  nu- 
merically by  averages,  and,  as  far  as  my  imperfect  results  go, 
they  confirm  the  view.  I  have  also  consulted  some  sagacious 
and  experienced  observers,  and,  after  deliberation,  they  concur 
in  this  view.  In  this  respect,  therefore,  tlie  species  of  the 
larger  genera  resemble  varieties,  more  than  do  the  species  of 
the  smaller  genera.  Or  the  case  may  be  put  in  another  way, 
and  it  may  be  said  that  in  the  larger  genera,  in  which  a  num- 
ber of  varieties  or  incipient  species  greater  than  the  average 
are  now  manufacturing,  many  of  the  species  already  manufac- 
tured still  to  a  certain  extent  resemble  varieties,  for  they  differ 
from  each  other  by  less  than  the  usual  amount  of  difference. 

Moreover,  the  species  of  the  large  genera  are  related  to 
each  other,  in  the  same  manner  as  the  varieties  of  any  one 
species  are  related  to  each  other.  No  naturalist  pretends  that 
all  the  species  of  a  genus  arc  equally  distinct  from  each  other ; 
they  may  generally  be  divided  into  sub-genera,  or  sections,  or 
lesser  groups.  As  Fries  has  well  remarked,  little  groups  of 
species  are  generally  clustered  like  satellites  around  certain 
other  species.  And  what  are  varieties  but  groups  of  forms, 
imequally  related  to  each  other,  and  clustered  round  certain 
forms — that  is,  round  their  parent-species  ?     Undoubtedly  there 


Chap.  II.  RESEMBLE  VARIETIES.  07 

is  one  most  important  point  of  dilFerencc  between  varieties  and 
species ;  namely,  that  the  amount  of  diflerencc  between  varieties, 
M'hen  compared  with  each  other  or  with  their  parent-species,  is 
much  less  than  that  betw'een  the  species  of  the  same  genus.  But 
■when  WG  come  to  discuss  the  principle,  as  I  call  it,  of  Diver- 
gence of  Character,  we  shall  see  how  this  may  be  explained, 
and  how  the  lesser  diiferences  between  varieties  tend  to  in- 
crease into  the  greater  differences  between  species. 

There  is  one  other  point  which  is  worth  notice.  Varieties 
generally  have  much-restricted  ranges  :  this  statement  is  in- 
deed scarcely  more  than  a  truism,  for,  if  a  variety  were  found 
to  have  a  wider  range  thaii  that  of  its  sujiposed  parent-species, 
their  denominations  would  be  reversed.  But  there  is  also 
reason  to  believe  that  those  species  which  are  very  closely 
allied  to  other  species,  and  in  so  far  resemble  varieties,  often 
have  much-restricted  ranges.  For  instance,  Mr.  II.  C.  Watson 
has  marked  for  me,  in  the  well-sifted  London  Catalogue  of 
plants  (fourth  edition),  G3  plants  which  are  therein  ranked  as 
species,  but  which  he  considers  as  so  closely  allied  to  other 
species  as  to  be  of  doubtful  value :  these  63  reputed  species 
range  on  an  average  over  G.9  of  the  provinces  into  which  Mr. 
Watson  has  divided  Great  Britain.  Now,  in  this  same  cata- 
logue, 53  acknowledged  varieties  are  recorded,  and  these  range 
over  7.7  jirovinces  ;  whereas,  the  species  to  Avhich  these  vari- 
eties belong  range  over  14.3  provinces.  So  that  the  acknowl- 
edged varieties  have  very  nearly  the  same  restricted  average 
range  as  have  those  very  closely  allied  forms,  marked  for  me 
liy  Mr.  Watson  as  doubtful  species,  but  which  are  almost  uni- 
versally ranked  by  British  botanists  as  good  and  true  species. 

Summart/. 

Finally,  then,  varieties  caimot  be  distinguished  from  species 
— except,  first,  by  the  discovery  of  intermediate  linking  forms; 
and,  secondly,  by  a  certain  indefinite  amount  of  difference  be- 
tween them ;  for  two  forms,  if  differing  very  little,  are  gener- 
ally ranked  as  varieties,  notwithstanding  that  they  cannot  be 
closely  connected ;  but  the  amount  of  difference  considered 
necessary  to  give  to  any  two  forms  the  rank  of  species  cannot 
be  defined.  In  genera  having  more  than  the  average  number 
of  species  in  any  country,  the  species  of  these  genera  have 
more  than  the  average  number  of  varieties.  In  large  genera 
the  species  are  apt  to  be  closely,  but  uncfiually,  allied  together. 


68  SUMMARY.  Chap.  II. 

forming  little  clusters  round  certain  other  species.  Species 
very  closoly  allied  to  other  species  apparently  have  restricted 
rang'cs.  In  all  these  several  respects  the  species  of  large  genera 
present  a  strong  analogy  with  varieties.  And  we  can  clearly 
understand  these  analogies,  if  species  once  existed  as  varieties, 
and  thus  originated ;  whereas,  these  analogies  are  utterly  in- 
explicable if  species  are  independent  creations. 

We  have,  also,  seen  that  it  is  the  most  nourishing  or  dom- 
inant species  of  the  larger  genera  within  each  class  which  on 
an  average  3'ield  the  greatest  number  of  varieties ;  and  varie- 
ties, as  we  shall  hereafter  see,  tend  to  become  converted  into 
new  and  distinct  species.  Thus  the  larger  genera  tend  to  be- 
come larger ;  and  throughout  Nature  the  forms  of  life  which 
are  now  dominant  tend  to  become  still  more  dominant  by  leav- 
ing many  modified  and  dominant  descendants.  But  by  steps 
hereafter  to  be  explained,  the  larger  genera  also  tend  to  break 
up  into  smaller  genera.  And  thus,  the  forms  of  life  through- 
out the  universe  become  divided  into  groups  subordhiate  to 
groups. 


Chap.  III.  STRUGGLE  FOB  EXISTENCE.  69 


CHAPTER  III. 

STRUGGLE    FOR   EXISTENCE. 

Its  bearing  on  Natural  Selection— The  Term  used  In  a  wide  Sense— Geometrical  Ratio 
oriucroase — Rapid  Iiicreaao  of  Nuturalized  Animals  and  Plants— Nature  of  tho 
Checks  to  Incroase— Competition  universal— EftectR  of  Climate — Protection  from 
the  Number  of  Individuals — Complex  Relations  of  all  Animals  and  Plants  throush- 
out  Nature— St ru;;srlo  for  Life  most  severe  between  Individuals  and  Varieties  of 
the  same  *Specics:  often  severe  between  Species  of  the  same  Genus — The  Rela- 
tion of  Organism  to  Or^^anism  the  most  important  of  all  Relations. 

Before  entering  on  the  subject  of  this  chapter,  I  must 
make  a  few  prehminary  remarks,  to  show  how  the  struggle  for 
existence  bears  on  Natural  Selection.  It  has  been  seen  in  the 
last  chapter  that  among  organic  beings  in  a  state  of  nature 
there  is  some  individual  variability :  indeed,  I  am  not  aware 
that  this  has  ever  been  disputed.  It  is  immaterial  for  us 
whether  a  multitude  of  doubtful  forms  be  called  species  or 
sub-species  or  varieties ;  what  rank,  for  instance,  the  two  or 
three  hundred  doubtful  forms  of  British  plants  are  entitled  to 
hold,  if  the  existence  of  any  well-marked  varieties  be  admitted. 
But  the  mere  existence  of  individual  variability  and  of  some 
few  well-marked  varieties,  though  necessary  as  the  foundation 
for  the  work,  helps  us  but  little  in  understanding  how  species 
arise  in  Nature.  How  have  all  those  exquisite  adaptations  of 
one  part  of  the  organization  to  another  part,  and  to  the  condi- 
tions of  life,  and  of  one  organic  being  to  another  being,  been 
perfected  ?  We  see  these  beautiful  coadaptations  most  plain- 
ly in  the  woodpecker  and  the  mistletoe  ;  and  only  a  little  less 
])lainly  in  the  hinnblest  parasite  which  clings  to  the  hairs  of  a 
quadruped  or  feathers  of  a  bird;  in  the  structure  of  the  beetle 
wliich  dives  through  the  water ;  in  the  ])lumed  seed  which  is 
wafted  by  the  gentlest  breeze ;  in  short,  we  see  beautiful 
adaptations  everywhere  and  in  every  part  of  the  organic 
world. 

Again,  it  may  be  asked,  how  is   it  that  varieties,  which  I 
have  called  incipient  species,  become  ultimately  converted  into 


70  STRUGGLE  FOR  EXISTENCE.  Cuap.  III. 

good  and  distinct  species,  which  in  most  cases  obviously  differ 
from  each  oilier  far  more  than  do  the  varieties  of  the  same 
species?  How  do  those  groups  of  species,  wliich  constitute 
what  are  called  distinct  genera,  and  which  differ  from  each 
other  more  than  do  the  species  of  the  same  genus,  arise  ?  All 
these  results,  as  we  shall  more  fully  see  in  the  next  chapter, 
follow  from  the  struggle  for  life.  0\\4ng  to  this  struggle, 
variations,  however  slight,  and  from  whatever  cause  proceed- 
ing, if  they  be  in  any  degree  profitable  to  the  individuals  of  a 
species,  in  their  infinitely  complex  relations  to  other  organic 
beings  and  to  their  physical  conditions  of  life,  will  tend  to  the 
preservation  of  such  individuals,  and  will  generally  be  inherited 
by  the  offspring.  The  offspring,  also,  wUl  thus  have  a  better 
chance  of  surviving,  for,  of  the  many  individuals  of  an}^  species 
Avhich  are  periodically  born,  but  a  small  number  can  survive. 
I  have  called  this  principle,  by  which  each  slight  variation,  if 
useful,  is  preserved,  by  the  term  Natural  Selection,  in  order  to 
mark  its  relation  to  man's  power  of  selection.  But  the  expres- 
sion often  used  by  Mr.  Herbert  Spencer  of  the  Survival  of  the 
Fittest  is  more  accurate,  and  is  sometimes  equally  convenient. 
'SVe  have  seen  that  man  by  selection  can  certainly  produce 
great  results,  and  can  adapt  organic  beings  to  his  own  uses, 
through  the  accumulation  of  slight  but  useful  variations,  given 
to  him  by  the  hand  of  Nature.  But  Natural  Selection,  as  we 
shall  hereafter  see,  is  a  power  incessantly  ready  for  action,  and 
is  as  immeasurably  superior  to  man's  feeble  efforts  as  the 
works  of  Nature  are  to  those  of  Art. 

We  will  now  discuss  in  a  little  more  detail  the  struggle  for 
existence.  In  my  future  work  this  subject  will  be  treated,  as 
it  well  deserves,  at  greater  length.  The  elder  De  Candolle 
and  Ijyell  have  largely  and  philosophically  shown  that  all 
organic  beings  are  exposed  to  severe  competition.  In  regard 
to  plants,  no  one  has  treated  this  subject  Avith  more  spirit  and 
ability  than  AV.  Herbert,  Dean  of  Manchester,  evidently  the 
result  of  his  great  horticultural  knowledge.  Nothing  is  easier 
than  to  admit  in  words  the  truth  of  the  universal  struggle  for 
life,  or  more  difficult — at  least  I  have  found  it  so — than  con- 
stantly to  bear  this  conclusion  in  mind.  Yet  unless  it  be 
thoroughly  engrained  in  the  mind,  the  whole  economy  of 
Nature,  with  every  fact  on  distriljution,  rarity,  abundance,  ex- 
tinction, and  variation,  will  be  dimly  seen  or  quite  misunder- 
stood. We  behold  the  face  of  Nature  bright  Avith  gladness, 
Ave  often  sec  superabundance  of  food  ;  Ave  do  not  see,  or  Ave 


CuAP.  HI.  GEOMETRICAL  KATIO  OF  INCREASE.  71 

forget,  tliat  the  birds  which  arc  idly  singing  round  us  mostly 
live  on  insects  or  seeds,  and  are  thus  constantly  destroying 
life  ;  or  we  forget  how  largely  these  songsters,  or  their  eggs, 
or  their  nestlings,  are  destroyed  by  birds  and  beasts  of  prey  ; 
we  do  not  always  bear  in  mind,  that,  though  food  may  be  now 
superabundant,  it  is  not  so  at  all  seasons  of  each  recurring 
year. 

Tlie  2h'm,  Stu-uggle  for  Existence^  used  in  a  Large  Sense. 

I  should  premise  that  I  use  this  term  in  a  large  and  meta- 
phorical sense,  including  dependence  of  one  being  on  another, 
and  including  (which  is  more  important)  not  only  the  life  of 
the  indi\-idual,  but  success  in  lea\'ing  progeny.  Two  canine 
animals,  in  a  time  of  dearth,  may  be  truly  said  to  struggle  with 
each -other  which  shall  get  food  and  live.  But  a  plant  on  the 
edge  of  a  desert  is  said  to  struggle  for  life  against  the  drought, 
though  more  properly  it  should  be  said  to  be  dependent  on  the 
moisture.  A  plant  which  annually  produces  a  thousand  seeds, 
of  which  on  an  average  only  one  comes  to  maturity,  may  be 
more  truly  said  to  struggle  with  the  plants  of  the  same  and 
other  kinds  which  already  clothe  the  ground.  The  mistletoe 
is  dependent  on  the  apple  and  a  few  other  trees,  but  can  only 
in  a  far-fetched  sense  be  said  to  struggle  with  these  trees,  for, 
if  too  many  of  these  parasites  grow  on  the  same  tree,  it  will 
languish  and  die.  But  several  seedling  mistletoes,  growing 
close  together  on  the  same  branch,  may  more  truly  be  said  to 
struggle  with  each  other.  As  the  mistletoe  is  disseminated  by 
birds,  its  existence  depends  on  birds ;  and  it  may  metaphori- 
cally be  said  to  struggle  with  other  fruit-bearing  plants,  in 
order  to  tempt  birds  to  devour  and  thus  disseminate  its  seeds 
rather  than  those  of  other  plants.  In  these  several  senses, 
which  pass  into  each  other,  I  use  for  convenience'  sake  the 
general  term  of  struggle  for  existence. 

Geometrical  Ratio  of  Increase. 

A  struggle  for  existence  inevitably  follows  from  the  high 
rate  at  which  all  organic  beings  tend  to  increase.  Every  being 
which  during  its  natural  lifetime  produces  several  eggs  or 
seeds,  must  suffer  destruction  during  some  period  of  its  life, 
and  during  some  season  or  occasional  year,  otherwise,  on  the 
principle  of  geometrical  increase,  its  numbers  would   quickly 


72  GEOMETRICAL  RATIO  OF  INCREASE.  Chap.  III. 

become  so  inordinately  great  that  no  country  could  support  the 
product.  Hence,  as  more  individuals  are  produced  than  can 
possibly  survive,  there  must  in  every  case  be  a  struggle  for 
existence,  cither  one  individual  with  another  of  the  same  spe- 
cies, or  -with  the  individuals  of  distinct  species,  or  with  the  phys- 
ical conditions  of  life.  It  is  the  doctrine  of  Malthus  applied 
with  manifold  force  to  the  whole  animal  and  vegetable  king- 
doms ;  for  in  this  case  there  can  be  no  artificial  increase  of 
food,  and  no  prudential  restraint  for  marriage.  Although  some 
species  may  be  now  increasing,  more  or  less  rapidly,  in  num- 
bers, all  cannot  do  so,  for  the  world  would  not  hold  them. 

There  is  no  exception  to  the  rule  that  every  organic  being 
naturally  increases  at  so  high  a  rate,  that,  if  not  destroyed,  the 
earth  would  soon  be  covered  by  the  progeny  of  a  single  pair. 
Even  slow-breeding  man  has  doubled  in  twenty-five  years,  and 
at  this  rate,  in  a  few  thousand  years,  there  would  literally  not 
be  standing-room  for  his  progeny.  Linnasus  has  calculated 
that  if  an  annual  plant  produced  only  two  seeds — and  there  is 
no  plant  nearly  so  unproductive  as  this — and  their  seedlings 
next  year  produced  two,  and  so  on,  then  in  twenty  years  thei'C 
would  be  a  million  plants.  The  elephant  is  reckoned  the 
slowest  breeder  of  all  known  animals,  and  I  have  taken  some 
pains  to  estimate  its  probable  minimum  rate  of  natural  increase: 
it  will  be  safest  to  assume  that  it  begins  breeding  when  thirty 
years  old,  and  go'es  on  breeding  till  ninety  years  old,  bringing 
forth  six  young  in  the  interval,  and  surviving  till  one  hundred 
years  old ;  if  this  be  so,  after  a  period  of  from  seven  hundred 
and  forty  to  seven  hundi'ed  and  fifty  years,  there  would  be  alive 
nearly  nineteen  million  elephants  descended  from  the  first  pair. 

But  we  have  better  evidence  on  this  subject  than  mere 
theoretical  calculations,  namely,  the  numerous  recorded  cases 
of  the  astonishingly  ra\nd  increase  of  various  animals  in  a  state 
of  nature,  "when  circumstances  have  been  favorable  to  them 
during  two  or  three  following  seasons.  Still  more  striking  is 
the  evidence  from  our  domestic  animals  of  many  kinds  which 
liave  run  wild  in  several  parts  of  the  world :  if  the  statements 
of  the  rate  of  increase  of  slow-breeding  cattle  and  horses  in 
South  America,  and  latterly  in  Australia,  had  not  been  well 
authenticated,  they  Avould  have  been  incredible.  So  it  is  with 
plants  :  cases  could  be  given  of  introduced  plants  which  have 
b(>come  common  throughout  whole  islands  in  a  period  of  less 
than  ten  years.  Several  of  the  plants,  such  as  the  caitloon, 
and  a  tall  thistle,  now  most  numerous  over  the  wide  plains  of 


CiiAP.  III.         GEOMETRICAL  RATIO  OF' INCREASE.  73 

La  Plata,  clothing  square  leagues  of  surface  almost  to  the  ex- 
clusion of  all  other  plants,  have  been  introduced  from  Europe  ; 
and  there  are  plants  which  now  range  in  India,  as  I  hear  from 
Dr.  Falconer,  from  Cape  Comorin  to  tlie  Himalaya,  which  have 
been  imported  from  xVmerica  since  its  discovery.  In  such 
cases,  and  endless  instances  could  be  given,  no  one  supposes 
that  the  fertility  of  these  animals  or  phuits  has  been  suddenly 
and  temporarily  increased  in  any  sensil)le  degree.  The  obvious 
explanation  is  that  the  conditions  of  lifeliave  been  very  favor- 
able, and  that  there  has  consequently  been  less  destruction  of 
the  old  and  3'oung,  and  that  nearly  all  the  young  have  been 
enabled  to  breed.  In  such  cases  the  geometrical  ratio  of  in- 
crease, the  result  of  which  never  fails  to  be  surprising,  simply 
explains  the  extraordinarily  rapid  increase  and  wide  diffusion 
of  naturalized  productions  in  their  new  homes. 

In  a  state  of  nature  almost  every  plant  produces  seed,  and 
among  animals  there  are  very  few  which  do  not  annually  pair. 
Hence  we  may  confidently  assert,  that  all  plants  and  animals 
are  tending  to  increase  at  a  geometrical  ratio — that  all  would 
most  rapidly  stock  every  station  in  which  they  could  anjdiow 
exist — and  that  the  geometrical  tendency  to  increase  must  be 
checked  by  destruction  at  some  period  of  life.  Our  familiarity 
with  the  larger  domestic  animals  tends,  I  think,  to  mislead  us : 
Ave  see  no  great  destruction  falling  on  them,  and  we  forget  that 
thousands  are  annually  slaughtered  for  food,  and  that  in  a 
state  of  nature  an  equal  number  would  have  somehow  to  be 
disposed  of. 

The  only  difference  between  organisms  which  annually  pro- 
duce eggs  or  seeds  by  the  thousand,  and  those  which  produce 
extremely  few,  is,  that  the  slow-breeders  would  require  a  few 
more  years  to  people,  under  favorable  conditions,  a  Avliole  dis- 
trict, let  it  be  ever  so  large.  The  condor  lays  a  couple  of  eggs 
and  tlic  ostrich  a  score,  and  yet  in  the  same  country  the  condor 
may  be  the  more  numerous  of  the  two:  the  Fulmar  petrel  lays 
but  one  o<i;g,  yet  it  is  believed  to  be  the  most  numerous  bird  in 
the  world.  One  fly  deposits  hundreds  of  eggs,  and  another, 
like  the  hippolwsca,  a  single  one;  but  this  dillerence  does  not 
det(^nnine  how  many  individuals  of  the  two  species  can  be  sup- 
ported in  a  district.  A  large  nmnber  of  eggs  is  of  some  im- 
j)ortance  to  those  species  which  depend  on  a  rapidly-fluctuating 
amount  of  food,  for  it  allows  them  rapidly  to  increase  in  num- 
ber. 15ut  the  real  importance  of  a  large  number  of  eggs  or 
seeds  is  to  make  up  for  nuich  destruction  at  some  period  of  life  : 
4 


74  NATURE  OF  THE  CHECKS  TO  INCREASE.       Chap.  IIT, 

and  this  period  in  the  great  majority  of  cases  is  an  early  one. 
If  an  animal  can  in  any  way  protect  its  own  eggs  or  young,  a 
small  number  may  be  i)roduccd,  and  yet  the  average  stock  be 
fully  kept  up;  ])ut  if  many  eggs  or  young  are  dcstroj'ed,  many 
must  be  produced,  or  the  species  will  become  extinct.  It 
would  suilicc  to  keep  up  the  full  number  of  a  tree,  which  lived 
on  an  average  for  a  thousand  years,  if  a  single  seed  were  pro- 
duced once  in  a  thousand  years,  supposing  that  this  seed  were 
never  destroyed,  and  Could  lie  insured  to  germinate  in  a  fitting 
place.  So  that,  in  all  cases,  the  average  number  of  any  animal 
or  plant  depends  only  indirectly  on  the  number  of  its  eggs  or 
seeds. 

In  looking  at  Nature,  it  is  most  necessary  to  keep  the  fore- 
going considerations  always  in  mind  —  never  to  forget  that 
everj-  single  organic  being  around  us  may  be  said  to  be  striving 
to  the  utmost  to  increase  in  numbers ;  that  each  lives  by  a 
struggle  at  some  period  of  its  life  ;  that  hea\'y  destruction  in- 
evitably falls  either  on  the  young  or  old,  during  each  genera- 
tion or  at  recurrent  intervals.  Lighten  any  check,  mitigate 
the  destruction  ever  so  little,  and  the  number  of  the  species 
will  almost  instantaneously  increase  to  any  amount. 

Nature  of  the   Checks  to  Increase. 

The  causes  which  check  the  natural  tendency  of  each  spe- 
cies to  increase  are  most  obscure.  Look  at  the  most  vigorous 
species ;  by  as  much  as  it  swarms  in  numbers,  by  so  much  will 
its  tendency  to  increase  be  still  further  increased.  We  know 
not  exactly  what  the  checks  are  in  even  one  single  instance. 
Nor  will  this  surprise  any  one  who  reflects  hov/  ignorant  we 
are  on  this  head,  even  in  regard  to  mankind,  so  incomparably 
better  known  than  any  other  animal.  This  subject  has  been 
alily  treated  by  several  authors,  and  I  shall,  in  my  future  work, 
discuss  some  of  the  checks  at  considerable  length,  more  es- 
pecially in  regard  to  the  feral  animals  of  South  America.  Here 
I  will  make  only  a  few  remarks,  just  to  recall  to  the  reader's 
mind  some  of  the  chief  points.  Eggs  or  very  young  animals 
seem  genei-ally  to  sufler  most,  but  this  is  not  invariably  the 
case.  "With  plants  there  is  a  vast  destruction  of  seeds,  but, 
from  some  observations  which  I  have  made,  I  believe  that  it 
is  the  seedlings  which  sufier  most  from  germinating  in  ground 
iilrcvady  thickly  stocked  with  othcn-  jilants.  Seedlings,  also,  are 
destroyed  in  vast  numbers  by  various  enemies ;  for  instance. 


CiiAr.  III.        NATURE  OF  THE  CHECKS  TO  INCREASE.  75 

on  a  jiicco  of  ground  three  feet  long  and  two  wide,  dug  and 
cleared,  and  wliere  there  could  be  no  choking  from  other  plants, 
I  marked  all  the  seedlings  of  our  native  weeds  as  they  came 
up,  and  out  of  the  357  no  less  than  295  were  destroyed,  chielly 
by  slugs  and  insects.  If  turf  which  has  long  been  mown,  and 
the  case  would  be  the  same  with  turf  closely  browsed  by  quad- 
rupeds, be  let  to  grow,  the  more  vigorous  plants  gradually 
kill  the  less  vigorous  though  fully-grown  plants ;  thus  out  of 
twenty  species  growing  on  a  little  plot  of  turf  (three  feet  by 
four)  nine  species  perished  from  the  other  species  being  allowed 
to  grow  up  freely. 

The  amount  of  food  for  each  species  of  course  gives  the 
extreme  limit  to  which  each  can  increase  ;  but  very  frequently 
it  is  not  the  obtaining  food,  but  the  serving  as  prey  to  other 
animals,  which  determines  the  average  numbers  of  a  species. 
Thus',  there  seems  to  be  little  doubt  that  the  stock  of  par- 
tridges, grouse,  and  hares,  on  any  large  estate  depends  chiefly 
on  the  destruction  of  vermin.  If  not  one  head  of  game  were 
shot  during  the  next  twenty  years  in  England,  and,  at  the 
same  time,  if  no  vermin  were  destroyed,  tliere  would,  in  all 
prnba])ility,  be  less  game  tlian  at  present,  although  hundreds 
of  thousands  of  game  animals  are  now  annually  killed.  On  the 
other  hand,  in  some  eases,  as  with  the  elephant,  none  are  de- 
stroyed by  beasts  of  prey;  for  even  the  tiger  in  India  most 
larely  dares  to  attack  a  young  elephant  protected  by  its  dam. 

Climate  plays  an  important  part  in  determining  the  aver- 
ige  numbers  of  a  species,  and  periodical  seasons  of  extreme 
cold  or  drought  seem  to  be  the  most  effective  of  all  checks.  I 
estimated  (chiefly  from  the  greatly  reduced  numbers  of  nests 
in  the  sjiring)  that  the  winter  of  1854-55  destroyed  four-fifths 
of  the  birds  in  my  own  grounds ;  and  this  is  a  tremendous 
destruction,  when  we  remember  that  ten  per  cent,  is  an  ex- 
traordinarily severe  mortality  from  epidemics  with  man.  The 
action  of  climate  seems  at  first  sight  to  be  quite  independent 
of  the  struggle  for  existence  ;  but  in  so  far  as  climate  cliiefly 
acts  in  reducing  food,  it  brings  on  the  most  severe  struggle 
between  the  individuals,  whether  of  the  same  or  of  distinct 
species,  which  subsist  on  the  same  kind  of  food.  Evon  when 
climate,  for  instance  extreme  cold,  acts  directly,  it  will  be  the 
least  vigorous,  or  thost;  whicli  have  got  least  i'ood  through  the 
advancing  winter,  which  will  suffer  most.  "When  we  travel 
from  south  to  north,  or  from  a  damp  region  to  a  dry,  we  in- 
variidily  sec  some  species  gradually  getting  rarer  and  rarer, 


•J  6  NATURE  OF  THE  CHECKS  TO  INCPwEASE.      Chap.  III. 

and  finally  disappearing- ;  and  the  change  of  climate  being  con- 
spicuous, we  are  tempted  to  attribute  the  whole  effect  to  its 
direct  action.  But  tliis  is  a  false  view :  we  forget  that  each 
species,  even  where  it  most  abounds,  is  constantly  suffering 
enormous  destruction  at  some  period  of  its  life,  from  enemies 
or  from  competitors  for  the  same  place  and  food;. and  if  these 
enemies  or  competitors  be  in  the  least  degree  favored  by  any 
slight  change  of  climate,  they  will  increase  in  numbers,  and, 
as  each  area  is  aheady  fully  stocked  with  inhabitants,  the  other 
species  will  decrease.  "\\Tien  we  travel  southward  and  see  a 
species  decreasing  in  numbei"s,  Ave  may  feel  sure  that  the  cause 
lies  quite  as  much  in  other  species  being  favored,  as  in  tliis 
one  being  hurt.  So  it  is  when  we  travel  northward,  but  in  a 
somewhat  lesser  degree,  for  the  number  of  species  of  all  kinds, 
and  therefore  of  competitors,  decreases  northward;  hence,  in 
going  northward,  or  in  ascending  a  mountain,  we  far  oftener 
meet  with  stvuited  forms,  due  to  the  directly  injurious  action 
of  climate,  than  we  do  in  proceeding  southward  or  in  descend- 
ing a  mountain.  When  we  reach  the  Arctic  regions,  or  snow- 
capped summits,- or  absolute  deserts,  the  struggle  for  life  is 
almost  exclusively  with  the  elements. 

That  climate  acts  in  main  part  indirectly  by  favoring  other 
species,  Ave  may  clearly  see  in  the  prodigious  number  of  plants 
in  our  gardens  which  can  perfectly  Avell  endure  our  chmate, 
l)ut  which  never  become  naturalized,  for  they  cannot  compete 
with  om-  native  plants,  nor  resist  destmction  by  our  native 
animals. 

When  a  species,  owing  to  highly  favorable  circumstances, 
increases  inordinately  in  numbers  in  a  small  tract,  epidemics — 
at  least  this  seems  generally  to  occur  with  our  game  animals — 
often  ensue :  and  here  we  have  a  limiting  check  independent 
of  the  struggle  for  life.  But  even  some  of  these  so-called 
epidemics  appear  to  be  due  to  parasitic  worms,  which  have 
from  some  cause,  possibly  in  jiart  through  facihty  of  diffusion 
among  the  crowded  animals,  l)ecn  disproportionally  favored ; 
and  here  comes  in  a  sort  of  sti-uggle  between  the  parasite  and 
its  prey. 

On  the  other  hand,  in  many  cases,  a  large  stock  of  individ- 
uals of  the  same  species,  relatively  to  the  numbers  of  its  ene- 
mies, is  absolutely  necessary  for  its  preservation.  Thus  we  can 
easily  raise  plenty  of  corn  and  rape-seed,  etc.,  in  our  fields,  be- 
cause the  seeds  are  in  great  excess  compared  with  the  mnnber 
of  birds  which  feed  on  them ;  nor  can  the  birds,  though  liavinq 


Chap.  III.  STRUGGLE  FOR  EXISTENCE.  77 

a  superabundance  of  food  at  tliis  one  season,  increase  in  num- 
ber proportionally  to  the  supply  of  seed,  as  their  numbers  are 
checked  during  -winter ;  but  any  one  who  has  tried,  knows 
how  troublesome  it  is  to  get  seed  from  a  few  wheat  or  other 
such  plants  in  a  garden :  I  have  in  this  case  lost  every  single 
seed.  This  view  of  the  necessity  of  a  large  stock  of  the  same 
species  for  its  preservation,  explains,  I  believe,  some  singular 
facts  in  Nature,  such  as  that  of  very  rare  plants  being  some- 
times extremely  abundant  in  the  few  spots  where  they  do 
occur;  and  that  of  some  social  plants  being  social,  that  is, 
abounding  in  individuals,  even  on  the  extreme  confines  of  their 
range.  For  in  such  cases,  we  may  believe,  that  a  plant  could 
exist  only  where  the  conditions  of  its  life  were  so  favorable 
that  many  could  exist  together,  and  thus  save  the  species  from 
utter  destruction.  I  should  add  that  the  good  effects  of  fre- 
quent intercrossing,  and  the  ill  eff'ects  of  close  interbreeding, 
probably  come  into  play  in  some  of  these  cases ;  but  on  tliis 
intricate  subject  I  will  not  here  enlarge. 

Complex  Relations  of  all  Animals  and  Plants  to  each  other 
in  the  Struggle  for  Existence. 

Many  cases  are  on  record  showing  how  complex  and  unex- 
pected are  the  checks  and  relations  between  organic  beings, 
which  have  to  struggle  together  in  the  same  country.  I  will 
give  only  a  single  instance,  which,  though  a  simple  one,  has 
interested  me.  In  Staffordshire,  on  the  estate  of  a  relation, 
where  I  had  ample  means  of  investigation,  there  was  a  large 
and  extremely  barren  heath,  which  had  never  been  touched  by 
the  hand  of  man ;  but  several  hundred  acres  of  exactly  the 
same  nature  had  been  enclosed  twenty-five  years  previously 
and  planted  with  Scotch  fir.  The  change  in  the  native  vegeta- 
tion of  the  ])lanted  part  of  the  heath  was  most  remarkable, 
more  than  is  generally  seen  in  passing  from  one  quite  diiTerent 
soil  to  another;  not  only  the  proportional  numbers  of  the  heath- 
plants  were  wholly  changed,  but  twelve  species  of  j)lants  (not 
counting  grasses  and  carices)  flourished  in  the  plantations, 
which  could  not  be  found  on  the  heath.  The  effect  on  the 
insects  must  have  been  still  greater,  for  six  insectivorous  birds 
were  very  conmion  in  the  plantations,  which  were  not  to  be 
seen  on  the  heath ;  and  the  heath  was  frequented  by  two  or 
three  distinct  insectivorous  birds.  Here  we  see  how  potent 
has  been  the  cff"cct  of  the  introduction  of  a  single  tree,  nothing 


78  STEUGGLE  FOIi  EXISTENCE.  Cuap.  III. 

wliatever  Cise  liavinji^  been  clone,  "vvith  the  cxce}7tion  of  the 
huid  having  1)ecn  enclosed,  so  that  cattle  could  not  enter.  But 
how  important  an  clement  enclosure  is,  I  plainly  saw  near  Farn- 
ham,  in  Surrc}'.  Plcrc  there  are  extensive  heaths,  with  a  few 
clumps  of  old  Scotch  firs,  on  the  distant  hill-tops  :  within  the 
last  ten  j'ears  larg'e  spaces  have  been  enclosed,  and  self-sown 
firs  are  now  sprini!:iii2^  up  in  multitudes,  so  close  together  that 
all  cannot  live.  When  I  ascertained  that  these  young  trees 
had  not  been  sown  or  planted,  I  was  so  much  surprised  at  their 
numbcre  that  I  went  to  several  points  of  view,  whence  I  could 
examine  hundreds  of  acres  of  the  unenclosed  heath,  and  liter- 
ally I  could  not  see  a  single  Scotch  fir,  except  the  old  planted 
clumps.  But  on  looking  closely  between  the  st^ms  of  the 
heath,  I  found  a  multitude  of  seedlings  and  little  trees,  which 
had  been  perpetually  browsed  down  by  the  cattle.  In  one 
square  yfu'd,  at  a  point  some  himdred  yards  distant  from  one 
of  the  old  clumps,  I  counted  thirty-two  little  trees ;  and  one 
of  them,  with  twenty-six  rings  of  growth,  had  during  many 
years  tried  to  raise  its  head  above  the  stems  of  the  heath,  and 
had  failed.  No  wonder  that,  as  soon  as  the  laud  was  enclosed, 
it  became  thickly  clothed  with  vigorously-growing  young  firs. 
Yet  the  heath  was  so  extremely  barren  and  so  extensive  that 
no  one  would  ever  have  imagined  that  cattle  would  have  so 
closely  and  effectually  searched  it  for  food. 

Here  we  see  that  cattle  absolutely  determine  the  existence 
of  the  Scotch  fir ;  but  in  several  parts  of  the  world  insects 
determine  the  existence  of  cattle.  Perhaps  Paraguay  offers 
the  most  curious  instance  of  this ;  for  here  neither  cattle  nor 
horses  nor  dogs  have  ever  run  wild,  though  they  swarm  south- 
ward and  northwai'd  in  a  feral  state  ;  and  ^Vzara  and  Pengger 
have  shown  that  this  is  caused  by  the  greater  number  in  Para- 
guay of  a  certain  fly,  which  lays  its  eggs  in  the  navels  of  these 
animals  when  first  born.  The  increase  of  these  flics,  numerous 
as  they  are,  must  be  habitually  checked  by  some  mean?,  proba- 
bly l)y  other  parasitic  insects.  Hence,  if  certain  insectivorous 
birds  were  to  decrease  in  Paraguay,  the  parasitic  insects  would 
probably  increase  ;  and  this  Avould  lesson  the  num])er  of  the 
navel-frequenting  flies — then  cattle  and  horses  would  become 
f(>ral,  and  this  would  certainly  greatly  alter  (as  indeed  I  have 
obseiTod  in  parts  of  South  America)  the  vegetation  :  this  again 
would  largely  aflect  the  insects;  and  this,  as  Ave  have  just  seen 
in  Staffordshire,  the  insectivorous  birds,  and  so  onward  in 
ever-increasing  circles  of  complexity.     We  began   this  scries 


CflAr.  III.  STRUGGLE  FOR  EXISTENCE.  79 

by  insectivorous  birds,  and  -we  have  ended  with  tlieni.  Not 
tliat  in  nature  the  rehitions  can  ever  be  as  simple  as  this.  Bat- 
tle within  battle  must  ever  be  recurring'  with  varying'  success  ; 
and  yet  in  the  long-run  the  forces  are  so  nicely  balanced,  that 
the  lace  of  Nature  remains  uniform  for  long  periods  of  time, 
tliough  assuredly  the  merest  trifle  would  often  give  the  victory 
to  one  organic  being  over  another.  Nevertheless,  so  profound 
is  our  ignorance,  and  so  high  our  presumption,  that  we  marvel 
when  we  hear  of  the  extinction  of  an  organic  being  ;  and,  as 
we  do  not  see  the  cause,  we  invoke  cataclysms  to  desolate  the 
world,  or  invent  laws  on  the  duration  of  the  forms  of  life  ! 

I  am  tempted  to  give  one  more  instance  showing  how 
plants  and  animals,  most  remote  in  the  scale  of  Nature,  are 
bound  together  by  a  web  of  complex  relations.  I  shall  here- 
after have  occasion  to  show  that  the  exotic  Lobelia  fulgens,  in 
this  part  of  England,  is  never  visited  by  insects,  and  conse- 
fiucntly,  from  its  peculiar  structure,  never  sets  a  seed.  Near- 
ly all  our  orchidaceous  plants  absolutely  require  the  visits  of 
insects  to  remove  their  pollen-masses  and  thus  to  fertilize  them. 
I  find  from  experiments  that  humble-bees  are  almost  indispen- 
sable to  the  fertilization  of  the  heart's-ease  (Viola  tricolor),  for 
other  bees  do  not  visit  this  flower.  I  have  also  found  that  the 
visits  of  bees  are  necessary  for  the  fertilization  of  some  kinds 
of  clover :  for  instance,  20  heads  of  Dutch  clover  (Trifolium 
repens)  yielded  2,290  seeds,  but  20  other  heads  protected  from 
bees  produced  not  one.  Again,  100  heads  of  red  clover  (T. 
pratense)  produced  2,700  seeds,  but  the  same  number  of  pro- 
tected heads  produced  not  a  single  seed.  Humble-bees  alone 
visit  red  clover,  as  other  bees  cannot  reach  the  nectar.  It  has 
been  suggested  that  moths  may  fertilize  the  clovers ;  but  I 
doubt  whether  they  could  do  so  in  the  case  of  the  red  clover, 
from  their  weight  not  being  sufficient  to  depress  the  wing- 
petals.  Hence  we  may  infer  as  highly  probable  that,  if  the 
whole  genus  of  humljle-bces  became  extinct  or  very  rare  in 
England,  ihe  heart's-ease  and  red  clover  would  become  very 
rare,  or  wholly  disappear.  The  number  of  humble-bees  in  any 
district  depends  in  a  great  degree  on  the  number  of  field-mice, 
which  destroy  their  combs  and  nests  ;  and  Colonel  Newman, 
who  has  long  attended  lo  the  habits  of  humble-bees,  believes 
that  "  more  than  two-thirds  of  them  are  thus  destroyed  all 
over  England."  Now  the  number  of  mice  is  hirgely  depend- 
ent, as  every  one  knows,  on  tlic  niunber  of  cats :  and  Colonel 
Newman  says,  "  Near  villages  and  small  towns  I  have  found 


80  STRUGGLE  FOK  EXISTENCE.  Chap.  ^ly, 

the  nests  of  humble-bees  more  numerous  than  elsewhere, Mhich 
I  attribute  to  the  number  of  cats  that  destroy  the  mice."  Hence 
it  is  quite  credible  that  the  presence  of  a  fefine  animal  in  large 
numbers  in  a  district  might  determine,  through  the  interven- 
tion first  of  mice  and  then  of  bees,  the  frequency  of  certain 
flowers  in  that  district ! 

In  the  case  of  every  species,  many  different  checks,  acting 
at  diflerent  periods  of  life,  and  during  different  seasons  or 
years,  probably  come  into  play  ;  some  one  check  or  some  few 
being  generally  the  most  potent,  but  all  concur  in  determining 
the  average  number  or  even  the  existence  of  the  species.  In 
some  cases  it  can  be  shown  that  widely-different  checks  act  on 
the  same  species  in  different  districts.  When  we  look  at  the 
jilants  and  bushes  clothing  an  entangled  bank,  Ave  are  tempted 
to  attribute  their  proportional  numbers  and  kinds  to  what  we 
call  chance.  But  how  false  a  view  is  this  !  Every  one  has 
heard  that  when  an  American  forest  is  cut  down,  a  very  differ- 
ent vegetation  springs  up ;  but  it  has  been  observed  that  an- 
cient Indian  ruins  in  the  Southern  United  States,  which  must 
formerly  haA'e  been  cleared  of  trees,  now  display  the  same 
beavitiful  diversity  and  proportion  of  kinds  as  in  the  surround- 
ing virgin  forest.  What  a  struggle  must  have  gone  on  during 
long  centuries  betAveen  the  scA'cral  kinds  of  trees,  each  annual- 
ly scattering  its  seeds  by  the  thousand ;  Avhat  Avar  betAvcen 
insect  and  insect — between  insects,  snails,  and  other  animals, 
Avith  birds  and  beasts  of  pre}^ — all  striving  to  increase,  ail 
fcx'ding  on  each  other,  or  on  the  trees,  their  seeds  and  seed- 
lings, or  on  the  other  plants  Avhich  first  clothed  the  groimd 
and  thus  checked  the  groAvth  of  the  trees  !  ThroAV  vip  a  handful 
of  feathers,  and  all  must  fall  to  the  ground  according  to  defi- 
nite laAvs ;  but  Iioav  simple  is  the  jiroblem  Avhere  each  shall  fall 
compared  to  that  of  the  action  and  reaction  of  the  innumerable 
plants  and  animals  which  haA'C  determined,  in  the  course  of 
centuries,  the  proportional  numbers  and  kinds  of  trees  noAV 
ffroAving  on  the  old  Indian  ruins  ! 

The  dependency  of  one  organic  being  on  another,  as  of  a 
parasite  on  its  prey,  lies  generally  betAveen  beings  remote  in 
the  scale  of  nature.  This  is  likcAvise  sometimes  the  case  Avith 
those  Avhich  may  strictly  be  said  to  struggle  Avith  each  other 
for  existence,  as  in  the  case  of  locusts  and  grass-feeding  quad- 
rupeds. But  the  struggle  Avill  almost  invariably  be  most 
severe  betAveen  the  individuals  of  the  same  species,  for  they 
frequent  the  same  districts,   require  the  same  food,  and    are 


CiiAr.  111.  STRUGGLE  FOlt  EXISTENCE.  81 

exposed  to  the  same  dangers.  lu  the  case  of  vai-ietics  of  the 
same  species,  the  struggle  will  generally  be  almost  equally 
severe,  and  we  sometimes  see  the  contest  soon  decided :  for 
instance,  if  several  varieties  of  wheat  be  sown  together,  and 
the  mixed  seed  be  resown,  some  of  the  varieties  Avhich  best 
suit  the  soil  or  climate,  or  are  naturally  the  most  fertile,  Avill 
beat  the  others  and  so  yield  more  seed,  and  will  consequently 
in  a  few  years  quite  su^iplant  the  other  varieties.  To  keep  vip 
a  mixed  stock  of  even  such  extremely-close  varieties  as  the 
variously-colored  sweet-peas,  they  must  be  each  year  harvested 
separately,  and  the  seed  then  mixed  in  due  proportion,  other- 
wise the  weaker  kinds  Avill  steadily  decrease  in  number  and 
disappear.  So,  again,  with  the  varieties  of  sheep  :  it  has  licen 
asserted  that  certain  mountain-varieties  will  starve  out  other 
mountain-varieties,  so  that  they  cannot  be  kept  together.  The 
same  result  has  followed  from  keeping  together  different  varie- 
ties of  the  medicinal  leech.  It  may  even  be  doubted  whether 
the  varieties  of  any  of  our  domestic  plants  or  animals  have  so 
exactly  the  same  strength,  habits,  and  constitution,  that  the 
original  proportions  of  a  mixed  stock  could  be  kept  up  for  half 
a  dozen  generations,  if  they  were  allowed  to  struggle  together, 
like  beings  in  a  stUte  of  nature,  and  if  the  seed  or  young  were 
not  annually  sorted. 

'  Struggle  for  Life  most  severe  between  Individuals  and  Vari- 
eties of  the  same  Sjyecles. 

As  species  of  the  same  genus  have  usually,  though  by  no 
means  invariably,  much  similarity  in  habits  and  constitution, 
and  always  in  structure,  the  struggle  will  generally  be  more 
severe  between  species  of  the  same  genus,  when  they  come 
into  competition  Avith  each  other,  than  between  species  of  dis- 
tinct genera.  We  see  this  in  the  recent  extension  over  parts 
of  the  United  States  of  one  species  of  swallow  having  caused 
the  decrease  of  another  species.  The  recent  increase  of  the 
missel-thrush  in  parts  of  Scotland  has  caused  the  decrease  of 
the  song-thrush.  How  frequently  we  hear  of  one. species  of 
rat  taking  the  place  of  another  species  under  the  most  differ- 
ent climates  !  In  Russia  the  small  Asiatic  cockroach  has  every- 
where driven  before  it  its  great  congener.  In  Australia  the 
imported  hivG^bce  is  rapidly  exterminating  the  small,  .stingless 
native  bee.  One  species  of  charlock  has  been  known  to  sup- 
plant another  species ;  and  so  in  other  cases.    We  can  dimly 


82  STRUGGLE  FOR  EXISTENCE.  Cuap.  III. 

see  why  the  competition  should  be  most  severe  between  allied 
forms,  which  fill  nearly  the  same  place  in  the  economy  of  Na- 
ture ;  but  probably  in  no  one  case  could  "vve  precisely  say  why 
one  species  has  been  victorious  over  another  in  the  great  bat- 
tle of  life. 

A  corollary  of  the  highest  importance  may  be  deduced 
from  the  foregoing  remarks,  namely,  that  the  structure  of 
every  organic  being  is  related,  in  the  most  essential  yet  often 
hidden  manner,  to  that  of  all  the  other  organic  beings,  with 
"which  it  comes  into  competition  for  food  or  residence,  or  from 
which  it  has  to  escape,  or  on  which  it  preys.  This  is  obvious 
in  the  structure  of  the  teeth  and  talons  of  the  tiger ;  and  in 
that  of  the  legs  and  claws  of  the  parasite  which  clings  to  the 
hair  on  the  tiger's  body.  But  in  the  beautifully-plumed  seed 
of  the  dandehon,  and  in  the  flattened  and  fringed  legs  of  the 
water-beetle,  the  relation  seems  at  first  confined  to  the  ele- 
ments of  air  and  Avater.  Yet  the  advantage  of  plumed  seeds 
no  doubt  stands  in  the  closest  relation  to  the  land  being 
already  thickly  clothed  Avith  other  plants ;  so  that  the  seeds 
may  be  widely  distributed  and  fall  on  iinoccupied  ground.  In 
the  water-beetle,  the  structm-e  of  its  legs,  so  well  adapted  for 
diving,  allows  it  to  compete  with  other  a'quatic  insects,  to 
hunt  for  its  own  prey,  and  to  escape  ser\dng  as  prey  to  other 
animals. 

The  store  of  nutriment  laid  up  witliin  the  seeds  of  many 
plants  seems  at  first  sight  to  have  no  sort  of  relation  to  other 
jilants.  But  from  the  strong  growth  of  young  plants  produced 
from  such  seeds  (as  peas  and  beans),  when  sown  in  the  midst 
of  long  grass,  it  may  be  suspected  that  the  chief  use  of  the 
luitriment  in  the  seed  is  to  favor  the  growth  of  the  young  seed- 
ling, while  struggling  with  other  plants  growing  vigorously 
all  around. 

Look  at  a  plant  in  the  midst  of  its  range,  why  does  it  not 
double  or  qviadruplc  its  nimibers  ?  We  know  that  it  can  per- 
fectly well  withstand  a  little  more  heat  or  cold,  dampness  or 
dryness,  for  elsewhere  it  ranges  into  slightly  hotter  or  colder, 
damper  or  drier  districts.  In  this  case  we  can  clearly  sec  that 
if  we  wished  in  imagination  to  give  the  plant  the  power  of  in- 
creasing in  number,  we  should  have  to  give  it  some  advantage 
over  its  competitors,  or  over  the  aTiimals  which  jireyed  on  it. 
( )n  the  confines  of  its  geographical  range,  a  change  of  consti- 
tution Avith  respect  to  climate  would  clearly  be  an  advan- 
tage to  our  plant ;  but  we  have  reason  to  believe  that  only  a 


Chap.  III.  STKUGGLE  FOR  EXISTENCE.  83 

few  plants  or  aniniiils  rani]fc  so  far,  that  tbcy  are  destroyed  by 
the  rigor  of  the  climate  alone.  Not  until  we  reach  the  extreme 
confines  of  life,  in  the  Arctic  regions  or  on  the  borders  of  an 
utter  desert,  will  competition  cease.  The  land  may  be  ex- 
tremely cold  or  dry,  yet  there  will  be  competition  between 
some  few  species,  or  between  the  individuals  of  the  same  spe- 
cies, for  the  Avarmest  or  dampest  spots. 

Hence,  also,  we  can  see  that  when  a  plant  or  animal  is 
placed  in  a  new  country  among  new  competitors,  tliough  the 
climate  may  be  exactly  the  same  as  in  its  former  home,  yet 
the  conditions  of  its  life  will  generally  be  changed  in  an  essen- 
tial manner.  If  we  wished  to  increase  its  average  numbers  in 
its  new  home,  we  should  have  to  modify  it  in  a  diflerent  way 
to  what  we  should  have  to  do  in  its  native  country;  for  we 
should  have  to  give  it  some  advantage  over  a  different  set  of 
convpetitors  or  enemies. 

It  is  good  thus  to  try  in  imagination  to  give  any  form 
some  advantage  over  another.  Probably  in  no  single  instance 
should  we  know  what  to  do,  so  as  to  succeed.  It  will  con- 
A-ince  us  of  our  ignorance  on  the  mutual  relations  of  all  organic 
beings  ;  a  conviction  as  necessar}',  as  it  seems  difficult  to  ac- 
quire. All  that  we  can  do  is,  to  keep  steadily  in  mind  that 
each  organic  being  is  striving  to  increase  in  a  geometrical 
ratio ;  that  each  at  some  period  of  its  life,  during  some  season 
of  the  year,  during  each  generation  or  at  intervals,  has  to 
struggle  for  life,  and  to  suffer  great  destruction.  When  we 
reflect  on  this  struggle,  we  may  console  ourselves  with  the  full 
belief  that  the  war  of  Nature  is  not  incessant,  that  no  fear  is 
felt,  that  death  is  generally  jirompt,  and  that  the  vigorous,  the 
healthy,  and  the  haj^py,  survive  and  multiply. 


84  NATUEAL  SELECTION.  Ciiap.  IV. 


•      CHAPTER  IV. 

NATURAL   SELECTION,    OK   THE    SURVIVAL   OF   THE   FITTEST. 

Natural  Selection— its  Power  compared  with  jMan's  Selection— its  Power  on  Char- 
acters of  trifling  Importance— its  Power  at  all  A<;e8  and  on  both  Soxes— Sexual 
Selection— On  the  CJenenility  of  Intercrosses  between  Individuals  of  the  same 
Species — Circumstances  favorable  and  unfavorable  to  the  Results  of  Natural  Se- 
lection, namely.  Intercrossing:,  Isolation,  Nnnibor  of  Individuals — Slow  Action — 
Extinction  caused  by  Natural  Selection— Divergence  of  Character  related  to  the 
Diversity  of  Inhabitants  of  any  Small  Area,  and  to  Naturalization— Action  of  Nat- 
ural Selection,  through  Divergence  of  Character  and  Extinction,  on  the  Descend- 
ants from  a  C(<mmou  Parent— Explains  the  Grouping  of  all  Organic  Heings— Ad- 
vance in  Organization — Low  Forms  preserved — Objections  considered— Uniform- 
ity of  certain  Characters  due  to  their  Unimportance  and  to  their  not  having  been 
acted  on  by  Natural  Selection— Indefinite  Multiplication  of  Species — Summary. 

How  will  the  struggle  for  existence,  briefly  discussed  in 
tlie  last  chapter,  act  in  regard  to  variation  ?  Can  the  principle 
of  selection,  which  we  have  seen  is  so  potent  in  the  hands  of 
man,  apply  in  Nature  ?  I  think  we  shall  see  that  it  can  act 
most  effectually.  Let  the  endless  number  of  peculiar  varia- 
tions in  our  domestic  productions,  and,  in  a  lesser  degree,  in 
those  under  Nature,  be  borne  in  ^ind ;  as  well  as  the  strength 
of  the  hereditary  tendency.  Under  domestication,  it  may  be 
tridy  said  that  the  Avliole  organization  becomes  in  some  degree 
plastic.  But  the  variability,  which  we  almost  universally  meet 
with  in  our  domestic  productions,  is  not  directly  produced,  as 
Hooker  and  Asa  Gray  have  well  remarked,  by  man ;  he  can 
neither  originate  varieties,  nor  prevent  their  occurrence ;  he 
can  onlv  preserve  and  acciunulate  such  as  do  occur;  uninten- 
tionally he  exjioses  organic  beings  to  new  and  changing  con- 
ditions of  life,  and  variability  ensues;  but  similar  changes  of 
conditions  might  and  do  occur  under  Nature.  Let  it  als«>  be 
borne  in  mind  how  inlinitely  complex  and  close-fitting  are  the 
mutual  relations  of  all  organic  beings  to  each  other  and  to 
tlieir  physical  conditions  of  life ;  and  consequently  what  in- 
finitely-varied diversities  of  structure  may  be  of  use  to  each 
l)cing  under  changing  conditions  of  life.  Can  it,  then,  be 
thought  improbable,  seeing  that  variations  usefid  to  man  have 
undoubtedly  occurred,  that  other  variations  useful  in  some  way 


CiiAP.  IV.  NATURAL  SELECTION.  85 

to  each  beinp^  in  the  frrcat  and  complex  battle  of  life,  sliouUl 
sometimes  occur  in  the  course  of  thousands  of  generations? 
If  such  do  occur,  can  we  doubt  (remembering'  that  many  more 
individuals  are  born  than  can  possibly  survive)  that  individuals 
having  any  advantage,  however  slight,  over  others,  would  have 
the  best  chance  of  surviving  and  of  procreating  their  kind  ? 
On  the  other  hand,  we  may  feel  sure  that  any  variation  in  the 
least  degree  injurious  would  be  rigidly  destroyed.  This  pres- 
ervation of  favorable  variations,  and  the  destruction  of  injuri- 
ous variations,  I  call  Natural  Selection,  or  the  Survival  of  the 
Fittest.  Variations  neither  useful  nor  injurious  would  not  be 
affected  by  natural  selection,  and  would  be  left  either  a  fluc- 
tuating element,  as  perhaps  we  see  in  certain  polymorphic 
species,  or  would  ultimately  become  fixed,  owing  to  the  nature 
of  the  organism  and  the  nature  of  the  conditions. 

Several  writers  have  misapprehended  or  objected  to  the 
tenn  Natural  Selection.  Some  have  even  imagined  that  nat- 
ural selection  induces  variability,  whereas  it  imphes  only  the 
preservation  of  such  variations  as  occur  and  are  beneficial  to 
the  being  under  its  conditions  of  life.  No  one  objects  to  agri- 
culturists speaking  of  the  potent  effects  of  man's  selection ;  and 
in  this  case  the  individual  differences  given  by  Nature,  which 
man  for  some  object  selects,  must  of  necessity  first  occur. 
Others  have  objected  that  the  term  selection  implies  conscious 
choice  in  the  animals  Avhich  become  modified;  and  it  has  even 
been  urged  that,  as  plants  have  no  volition,  natural  selection  is 
not  applicable  to  them !  In  the  literal  sense  of  the  word,  no 
doubt,  natural  selection  is  a  false  term ;  but  who  ever  objected 
to  chemists  speaking  of  the  elective  affinities  of  the  various 
elements  ? — and  yet  an  acid  cannot  strictl}^  be  said  to  elect  the 
base  with  which  it  in  preference  combines.  It  has  been  said 
that  I  speak  of  natural  selection  as  an  active  power  or  Deity  ; 
but  who  objects  to  an  author  speaking  of  the  attraction  of 
gravity  as  ruling  the  movements  of  the  planets  ?  Every  one 
knows  what  is  meant  and  is  implied  by  such  metaphorical  ex- 
])ressions ;  and  they  are  almost  necessary  for  brevity.  So, 
again,  it  is  difficult  to  avoid  personifying  the  word  Nature  ;  but 
I  mean  by  Nature,  only  the  aggregate  action  and  product  of 
many  natural  laws,  and  by  laws  the  sequence  of  events  as  as- 
certained by  us.  With  a  little  familiarity  such  superficial  ob- 
jections Avill  be  forgotten. 

We  shall  best  understand  the  probable  course  of  natural 
selection  by  taking  the  case  of  a   country  undergoing  some 


SG  NATURAL  SELECTION.  Chap.  IV. 

slii^ht  iihysical  chanire,  for  instance,  of  climate.  The  propor- 
tional numbers  of  its  inhabitants  -would  almost  immediately 
undergo  a  change,  and  some  species  might  become  extinct. 
AVe  may  conclude,  from  what  avc  have  seen  of  the  intimate 
and  complex  manner  in  which  the  inhabitants  of  each  country 
arc  boinid  together,  that  any  change  in  the  numerical  jiropor- 
tions  of  some  of  the  inhabitants,  independently  of  the  change 
of  climate  itself,  would  seriously  affect  the  others.  If  the 
country  were  open  on  its  borders,  new  fonns  would  certainly 
innnigrate,  and  this  also  would  often  seriously  disturb  the  re- 
lations of  some  of  the  former  inhabitants.  Let  it  be  remem- 
bered how  powerful  the  influence  of  a  single  introduced  tree 
or  mammal  has  been  sliOAvn  to  be.  But  in  the  case  of  an 
island,  or  of  a  country  partly  surrounded  by  barriers,  into 
which  new  and  better-adapted  forms  could  not  freely  enter,  we 
should  then  have  places  in  the  economy  of  Natvire  Avhich  would 
assuredly  be  better  fdled  up,  if  some  of  the  original  inhabitants 
were  in  some  manner  modified ;  for,  had  the  area  been  ojien  to 
immigration,  these  same  places  would  have  been  seized  by  in- 
truders. In  such  cases,  slight  modifications,  which  in  any  way 
favored  the  individuals  of  any  species,  by  better  adajiting  them 
to  their  altered  conditions,  would  tend  to  be  prcsen-ed ;  and 
natural  selection  would  have  free  scope  for  the  Avork  of  im- 
provement. 

We  have  reason  to  believe,  as  stated  in  the  first  chapter, 
that  changes  in  the  conditions  of  life  cause  or  excite  a  ten- 
dency to  vary ;  and  in  the  foregoing  case  the  conditions  are 
supposed  to  have  changed,  and  this  would  manifestly  be  favor- 
able to  natural  selection,  by  giving  a  better  chance  of  profit- 
able variations  occurring;  and  unless  such  do  occur,  natural 
selection  can  do  nothing.  Under  the  term  of  "variations,"  it 
must  never  be  forgotten  that  mere  individual  diflerences  are 
always  included.  As  man  can  certainly  ]noducc  a  great  result 
with  his  domestic  animals  and  plants  by  adding  up  in  any 
given  direction  individual  differences,  so  could  natural  selection, 
but  far  more  easily,  from  having  incomparably  longer  time  for 
action.  Nor  do  I  believe  that  any  great  physical  change,  as 
of  climate,  or  any  imusual  degree  of  isolation  to  check  immi- 
gration, is  actually  necessary  to  ])roduce  new  and  unoccujiied 
places  for  natural  selection  to  fill  up  by  modifying  and  im])rf)v- 
ing  some  of  the  A-arying  inhabitants.  For  as  all  the  inhabit- 
ants of  each  country  are  struggling  together  Avith  nic(^ly-bal- 
anccd  forces,  extremely-slight  modifications  in  the  structure  oi 


CnAi-.  IV.  NATURAL  SELECTION.  87 

habits  of  one  si)ecics  would  often  give  it  an  advantugc  over 
others  ;  and  still  further  modifications  of  the  same  liind  Avould 
often  still  further  increase  the  advantage,  as  long  as  the  species 
continued  under  the  same  conditions  of  life  and  profited  by 
similar  means  of  sul)sistence  and  defence.  No  country  can  be 
named,  in  which  all  the  native  inhabitants  are  now  so  perfectly 
adapted  to  each  other  and  to  the  physical  conditions  under 
which  they  live,  that  none  of  them  could  be  still  better  adapted 
or  improved ;  for,  in  all  countries,  the  natives  have  been  so  far 
conquered  by  naturalized  productions,  tliat  they  have  allowed 
foreigners  to  take  iirin  ])ossession  of  the  land.  And,  as  for- 
eigners have  thus  in  every  country  beaten  some  of  the  natives, 
Ave  may  safely  conclude  that  the  natives  might  have  been  mod- 
ified with  advantage,  so  as  to  have  better  resisted  the  in- 
truders. 

As  man  can  produce  and  certainly  has  produced  a  great 
result  by  his  methodical  and  unconscious  means  of  selection, 
what  may  not  natural  selection  effect  ?  Man  can  act  only  on 
external  and  visible  characters :  Nature,  if  I  may  be  allowed 
to  j)ersonify  the  natural  preservation  or  survival  of  the  fittest, 
cares  nothing  for  appearances,  except  in  so  far  as  they  are  use- 
ful to  any  being.  She  can  act  on  every  internal  organ,  on 
every  shade  of  constitutional  difference,  on  the  whole  machinery 
of  life.  Man  selects  only  for  his  own  good ;  Nature  only  for 
that  of  the  being  which  she  tends.  Every  selected  character  is 
fully  exercised  by  her,  as  is  implied  by  the  fact  of  their  selection. 
Man  keeps  the  natives  of  many  climates  in  the  same  country ; 
he  seldom  exercises  each  selected  character  in  some  peculiac 
and  fitting  manner  ;  he  feeds  a  long  and  a  short  beaked  pigeon 
on  the  same  food ;  he  does  not  exercise  a  long-backed  or  long- 
legged  quadrup(^(l  in  any  peculiar  manner ;  he  exposes  sheep 
with  long  and  short  wool  to  the  same  climate.  lie  does  not 
allow  the  most  vigorous  males  to  struggle  for  the  females.  He 
does  not  rigidly  destroy  all  inferior  animals,  but  protects  during 
each  varying  season,  as  far  as  lies  in  his  power,  all  his  produc- 
tions. He  often  begins  his  selection  by  some  half-monstrous 
form;  or  at  least  by  some  modification  prominent  enough  to 
catch  the  eye  or  to  be  plainly  useful  to  him.  Under  Nature, 
the  slightest  differences  of  structure  or  constitution  may  well 
turn  the  nicely-balanceil  scale  in  the  struggle  for  life,  and  so  be 
preserved.  How  fleet uig  are  the  wishes  and  eflbrts  of  man! 
how  short  his  time !  and  consequently  how  poor  will  be  his 
results,  comjiared  with  those  accumulated  l)y  Nature  during 


88  NATUKAL  SELECTION.  Chap.  IV. 

whole  geological  periods  !  Can  we  wonder,  then,  that  Nature's 
productions  should  be  far  "  truer  "  in  character  than  man's  pro- 
ductions ;  tliat  they  should  be  infinitely  better  adapted  to  the 
most  complex  conditions  of  life,  and  should  plainly  bear  the 
stamp  of  far  higher  workmanship? 

It  may  metaphorically  l)e  said  that  natural  selection  ig  daily 
and  hourly  scrutinizing,  throughout  the  world,  the  slightest  vari- 
ations ;  rejecting  those  that  are  bad,  preserving  and  adding  up 
all  that  are  good ;  silently  and  insensibly  working,  whenever 
and  wherever  opportunity  oft'ers,  at  the  improvement  of  each 
organic  being  in  relation  to  its  organic  and  inorganic  conditions 
of  life.  We  see  nothing  of  these  slow  changes  in  progress, 
until  the  hand  of  time  has  marked  tlie  lapse  of  ages,  and  then 
so  imperfect  is  our  view  into  long-past  geological  ages,  that 
we  see  only  that  the  forms  of  life  are  now  different  from  what 
they  formerly  were. 

In  order  that  any  great  amount  of  modification  in  any  part 
should  be  eflectcd,  a  variety  when  once  formed  must  again, 
perliaps  after  a  long  interval  of  time,  vary  or  present  individ- 
ual difl"erences  of  the  same  favorable  nature,  and  these  must  be 
again  preserved,  and  so  onward  step  by  step.  Seeing  that 
individual  differences  of  all  kinds  perpetually  recur,  this  can 
hardly  be  considered  as  an  unwarrantable  assumption.  But 
whether  all  this  has  actually  taken  place  must  be  judged  by 
how  far  the  h}q5othesis  accords  with  and  explains  tlie  general 
phenomena  of  Nature.  On  the  other  liand,  the  ordinary  belief 
that  the  amount  of  possible  variation  is  a  strictly-limited  quan- 
tity is  a  simple  assumption. 

Although  natural  selection  can  act  only  through  and  for  the 
good  of  each  being,  yet  characters  and  structures,  which  we 
'are  apt  to  consider  as  of  very  trifling  importance,  may  thus 
be  acted  on.  When  we  see  leaf-eating  insects  green,  and  bark- 
feeders  mottled-gray ;  the  alpine  ptarmigan  white  in  winter, 
the  red-grouse  the  color  of  heather,  avc  must  believe  that  these 
tints  are  of  service  to  these  birds  and  insects  in  preserving  them 
from  danger.  Grouse,  if  not  destroyed  at  some  period  of  their 
lives,  would  increase  in  countless  numbers ;  they  are  known  to 
suffer  largely  from  bii'ds  of  prey  ;  and  hawks  are  guided  by  eye- 
sight to  their  prey — so  much  so,  that  on  parts  of  the  Continent 
persons  are  warned  not  to  keep  white  pigeons,  as  being  the 
most  liable  to  destruction.  Hence  natural  selection  miglit  be 
most  eflective  in  giving  the  proper  color  to  each  kind  of  grouse, 
and  in  keeping  that  color,  when  once  acquired,  true  and  con 


CiiM-.  IV.  NATURAL  SELECTION.  89 

stant.  Nor  ougbt  we  to  think  that  the  occasional  destruction 
of  an  animal  of  any  particular  color  would  produce  little  effect : 
we  should  remember  how  essential  it  is  in  a  flock  of  white 
slicep  to  destroy  every  lamb  with  the  faintest  trace  of  black. 
A\'e  have  seen  how  the  color  of  the  ho<^s,  when  fcedino:  on  the 
"  paint-root "  in  Florida,  determines  whether  they  shall  live  or 
die.  In  plants  the  down  on  the  fruit  and  the  color  of  the  flesh 
are  considered  by  botanists  as  characters  of  the  most  trifling 
importance :  yet  we  hear  from  an  excellent  horticulturist,  Down- 
ing, that  in  the  United  States  smooth-skinned  fruits  sullcr  far 
more  from  a  beetle,  a  curculio,  than  those  Avith  down  ;  that  pur- 
ple plums  suffer  far  more  from  a  certain  disease  than  3X'llow 
plums  ;  whereas  another  disease  attacks  yellow-fleshed  peaches 
far  more  than  those  with  other  colored  flesh.  If,  with  all  the 
aids  of  art,  these  slight  differences  make  a  great  difl'crence  in 
cultivating  the  several  varieties,  assuredly,  in  a  state  of  nature, 
where  the  trees  would  have  to  struggle  with  other  trees  and 
with  a  host  of  enemies,  such  differences  would  effectually  settle 
whicli  variety,  whether  a  smooth  or  downy,  a  yellow  or  purple 
fleshed  fruit,  should  succeed. 

In  looking  at  many  small  points  of  difference  between  spe- 
cies, which,  as  far  as  our  ignorance  permits  us  to  judge,  seem 
quite  unimportant,  we  must  not  forget  that  climate,  food,  etc., 
may  have  produced  some  direct  eflect.  It  is  also  necessary  to 
bear  in  mind  that,  owing  to  the  law  of  correlation,  Avhen  one 
part  varies,  and  the  A\ariations  are  accumulated  through  natural 
selection,  other  modifications,  often  of  the  most  unexpected 
nature,  avUI  ensue. 

As  we  see  that  those  variations  Avhicli  under  domestication 
appear  at  any  particular  })eriod  of  life,  tend  to  rcapjwar  in  the 
offspring  at  the  same  period — for  instance,  in  the  shape,  size, 
and  flavor  of  the  seeds  of  the  many  varieties  of  our  culinary 
and  agricultural  plants  ;  in  the  caterpillar  and  cocoon  stages 
of  the  varieties  of  the  silk-worm ;  in  the  eggs  of  poultry,  and  in 
the  color  of  the  down  of  tlieir  chickens;  in  the  horns  of  our 
sheep  and  cattle  when  nearly  adult — so,  in  a  state  of  nature, 
natural  selection  Avill  be  enabled  to  act  on  and  modify  organic 
beings  at  any  age,  by  the  accumulation  of  variations  profitable 
j-t  that  age,  and  by  their  inheritance  at  a  corresponding  age. 
If  it  profit  a  plant  to  have  its  seeds  more  and  more  Avidely  dis- 
seminated by  the  wind,  I  can  sec  no  greater  difliculty  in  this 
being  effected  tlirough  natural  selection  than  in  the  cotton- 
planter  increasing  and  improving  by  selection  the  down  in  the 


DO  SEXUAL  SELECTION.  CriAr.  IV. 

pods  on  his  cotton-trces.  Natural  selection  may  modify  and 
adapt  the  larva  of  an  insect  to  a  score  of  continovncics,  wholly 
tlillcrent  from  tliose  which  concern  the  mature  insect;  and 
these  modilicalions  may  affect,  throug'h  correlation,  the  stnio 
ture  of  the  adult.  So,  conversely,  modifications  in  the  adult 
may  affect  tlie  structure  of  the  larva;  but  in  all  cases  natural 
selection  will  insure  that  they  shall  not  be  injurious:  for,  if 
they  were  so,  the  species  would  become  extinct. 

Natural  selection  will  modify  the  structure  of  the  young  in 
relation  to  the  parent,  and  of  the  parent  in  relation  to  the 
young.  In  social  animals  it  will  adapt  the  structure  of  each 
indivitlual  for  the  benefit  of  the  Avhole  community ;  if  this  in 
consequence  profits  by  the  selected  change.  What  natural 
selection  cannot  do,  is  to  modify  the  structure  of  one  species, 
without  giving  it  any  advantage,  for  the  good  of  another  spe- 
cies ;  and,  though  statements  to  this  effect  may  be  found  in 
works  of  natural  history,  I  cannot  find  one  case  which  will 
bear  investigation.  A  structure  used  only  once  in  an  animal's 
life,  if  of  high  importance  to  it,  might  be  modified  to  any  ex- 
tent by  natural  selection ;  for  instance,  the  great  jaws  pos- 
sessed by  certain  insects,  used  exclusively  for  opening  the 
cocoon — or  the  hard  tip  to  the  beak  of  nestling  birds,  used  for 
breaking  th(^  eir'^.  It  has  been  asserted  that,  of  the  best  short- 
lieaked  tumbler-pigeons,  a  greater  number  2:)erish  in  the  egg 
than  are  al^le  to  get  out  of  it ;  so  that  fanciers  assist  in  the  act 
of  hatching.  Now,  if  Nature  had  to  make  the  beak  of  a  full- 
j^rown  pigeon  very  short  for  the  bird's  own  advantage,  the  pro- 
cess of  modification  Avould  be  very  slow,  and  there  would  be 
simultaneously  the  most  rigorous  selection  of  all  the  young 
birds  within  the  egg,  which  had  the  most  powerful  and  hardest 
beaks,  for  all  with  weak  beaks  would  inevitably  perish ;  or, 
more  delicate  and  more  easily-l)rokcn  shells  might  be  se- 
lected, the  thickness  of  the  shell  being  knoAvn  to  vary  like 
every  other  structure. 

Sexual  Selection. 

Inasmuch  as  peculiarities  often  appear  under  domestication 
in  one  sex  and  become  hereditarily  attached  to  that  sex,  the 
same  fact  no  doubt  occurs  under  Nature,  and  if  so,  natural  se- 
lection will  be  able  to  modify  one  sex  in  its  functional  n'lations 
to  the  otlier  sex,  or  in  relation  to  Avholly-ditrerent  liabits  of  life 
in  the  two  sexes,  as  is  sometimes  the  case  with  insects.     And 


Chap.  IV.  SEXUAL  SELECTION.  91 

this  leads  ine  to  saj  a  few  words  on  what  I  call  Sexual  Selec- 
tion. This  depends,  not  on  a  sti'ugf^le  for  existence,  l)ut  on  a 
struo^g'lc  between  the  males  for  possession  of  tlie  females;  the 
result  is  not  death  to  the  inisuccessful  competitor,  but  few  or 
HO  oifsprino-.  Sexual  selection  is,  therefore,  less  rit^orous  than 
natural  selection.  Generally,  the  most  vigorous  males,  those 
\vhich  are  best  fitted  for  their  places  in  Nature,  will  leave  most 
progeny.  But,  in  many  cases,  victory  depends  not  on  general 
vigor,  but  on  having  special  weapons,  confined  to  the  male 
sex.  A  hornless  stag  or  spurless  cock  would  have  a  poor 
chance  of  leaving  numerous  ollspring.  Sexual  selection,  by 
always  allowing  the  victor  to  breed,  might  surely  give  indom- 
itable courage,  length  to  the  spur,  and  strength  to  the  wing 
to  strike  in  the  spurred  leg,  as  in  the  case  of  the  brutal  cock- 
fighter,  who  knows  well  how  to  improve  his  breed  hy  the  care- 
ful selection  of  the  best  cocks.  How  low  in  the  scale  of  Nature 
the  law  of  battle  descends,  I  know  not ;  male  alligators  have 
been  described  as  fighting,  bellowing,  and  Avhirling  round,  like 
Indians  in  a  war-dance,  for  the  possession  of  the  females  ;  male 
salmons  have  been  seen  fighting  all  day  long ;  male  stag-])eetles 
sometimes  bear  wounds  from  the  huge  mandibles  of  other 
mules  ;  tlie  males  of  certain  hymcnopterous  insects  have  been 
fivcjuently  seen  by  that  inimitable  observer  M.  Fabre,  fighting 
for  a  particular  female,  Avho  sits  by,  an  apparently  imcon- 
cerned  beholder  of  the  struggle,  and  then  retires  with  the  con- 
queror. The  war  is,  perhaps,  severest  between  the  males  of 
l)olygamous  animals,  and  these  seem  oftenest  provided  with 
special  weapons.  The  males  of  carnivorous  animals  arc  already 
well  armed  ;  though  to  them  and  to  others,  special  means  of  de- 
fence may  be  given  through  means  of  sexual  selection,  as  the 
mane  to  the  lion,  and  the  hooked  jaw  to  the  male  salmon;  for 
the  shield  may  be  as  important  for  victory  as  the  sword  or 
spear. 

Among  birds,  the  contest  is  often  of  a  more  peaceful  char- 
acter. All  those  who  have  attended  to  the  subject,  believe 
that  there  is  the  severest  rivalry  between  the  males  of  many 
species  to  attract  l)y  singing  the  females.  The  rock-thrush  of 
Guiana,  birds  of  Paradise,  and  some  others,  congregate;  and 
successive  males  display  tlieir  gorgeous  plumage  and  perform 
strange  antics  l)efore  the  females,  whieli,  standing  bv  as  spec- 
tators, at  last  choose  the  most  attractive  partner.  1'hose  who 
have  closely  attended  to  birds  in  confinement  well  know  that 
they  often  take  individual  preferences  and  dislikes:  thus  Sir 


02  ILLUSTRATIONS  OF  THE  ACTION   OF  Chap.  IV. 

Iv.  Iloroii  has  described  how  one  pied  peacock  was  eminently 
attractive  to  all  his  hen-birds.  I  cannot  here  enter  on  the  ne- 
cessary details ;  but  if  man  can  in  a  short  time  jjive  elegant 
carriage  and  beauty  to  his  bantams  according  to  liis  standard 
of  beauty,  I  can  see  no  good  reason  to  doubt  that  female 
birds,  by  selecting,  during  thousands  of  generations,  the  most 
melodious  or  beautiful  males,  according  to  their  standard  of 
beauty,  might  jiroduce  a  marked  effect.  Some  well-known 
laws,  with  respect  to  the  plumage  of  male  and  female  birds,  in 
comparison  with  the  plumage  of  the  young,  can  be  explained 
through  the  action  of  sexual  selection  on  variations  occurring 
at  diiierent  ages,  and  being  transmitted  to  the  males  alone  or 
to  both  sexes  at  a  corresponding  age  ;  but  I  have  not  space 
here  to  enter  on  this  "subject. 

Thus  it  is,  as  I  believe,  that  when  the  males  and  females  of 
any  animal  have  the  same  general  habits  of  life,  but  diller  in 
structure,  color,  or  ornament,  such  differences  have  been  main- 
ly caused  by  sexual  selection  ;  that  is,  by  individual  males  hav- 
ing had,  in  successive  generations,  some  slight  advantage  over 
other  males,  in  their  weapons,  means  of  defence,  or  charms ; 
and  having  transmitted  these  advantages  to  their  male  off- 
spring. Yet,  I  would  not  Avish  to  attribute  all  such  sexual  dif- 
ferences to  this  agency :  for  we  see  peculiarities  arising  and 
becoming  attached  to  the  male  sex  in  our  domestic  animals  (as 
the  greater  development  of  the  Avattle  in  male  carrier-pigeons, 
horn-like  protuberances  in  certain  fowls,  etc.),  Avhich  are  in  no 
way  useful.  We  see  analogous  cases  under  Nature — for  in- 
stance, the  tuft  of  hair  on  the  breast  of  the  turkej'-cock,  Avliich 
cannot  be  useful,  and  can  hardly  be  ornamental ;  indeed,  had 
the  tuft  appeared  under  domestication,  it  would  have  been 
called  a  monstrosity. 

Illustratio7is  of  the  Action  of  Natural  Selection,  or  the  Sur- 
vival of  the  Fittest. 

In  order  to  make  it  clear  how,  as  I  believe,  natural  selec- 
tion acts,  I  must  beg  permission  to  give  one  or  two  imaginary 
illustrations.  Let  us  take  the  case  of  a  wolf,  which  preys  on 
various  animals,  securing  some  by  craft,  some  by  strength,  and 
some  by  (leetness  ;  and  let  us  suppose  that  tlie  fleetest  prey, 
a  deer  for  instance,  had  from  any  change  in  the  country  in- 
creased in  numbers,  or  that  other  prey  had  decreased  in  num- 
bers, during  that  season  of  the  year  when  the  wolf  was  hardest 


CiiAP.  IV.  NATUKAL  SELECTION.  93 

pressed  for  food.  Under  such  cLrcumstances  the  swiftest  and 
slimmest  wolves  would  have  the  best  chance  of  survdving-,  and 
so  be  preserved  or  selected — provided  always  that  they  retained 
strength  to  master  their  prey  at  this  or  at  some  other  period 
of  the  year,  when  they  might  bo  compelled  to  prey  on  other 
animals.  I  can  see  no  more  reason  to  doubt  tliis,  than  that 
man  can  improve  the  fleetness  of  his  greyhounds  by  careful  and 
methodical  selection,  or  by  unconscious  selection  which  results 
from  each  man  trying  to  keep  the  best  dogs  without  any 
thought  of  modifying  the  breed.  I  may  add,  that,  according 
to  Mr.  Pierce,  there  are  two  varieties  of  the  wolf  inhabiting 
the  Catskill  Mountains  in  the  United  States,  one  with  a  light, 
greyhound-like  form,  which  pursues  deer,  and  the  other  more 
bulky,  with  shorter  legs,  which  more  frequently  attacks  the 
shepherd's  flocks. 

It  should  be  observed  that,  in  the  above  illustration,  I  speak 
of  the  slimmest  individual  wolves,  and  not  of  any  single  strong- 
Ij'-marked  variation  having  been  preserved.  In  former  editions 
of  this  work  I  sometimes  spoke  as  if  this  latter  alternative  had 
frequently  occurred.  I  saw  the  great  importance  of  individual 
differences,  and  this  led  me  fully  to  discuss  the  results  of  un- 
conscious selection  by  man,  which  depends  on  the  preservation 
of  the  better-adapted  or  more  valuable  individuals,  and  on  the 
destruction  of  the  worst.  I  saw,  also,  that  the  preservation  in 
a  state  of  nature  of  any  occasional  deviation  of  structure,  such 
as  a  monstrosity,  would  be  a  rare  event ;  and  that,  if  preserved, 
it  would  generally  be  lost  by  subsequent  intercrossing  with 
ordinary  individuals.  Nevertheless,  until  reading  an  able  and 
valuable  article  in  the  N'orth  Uritish  lievieio  (18G7),  I  did  not 
appreciate  how  rarely  single  variations,  whether  slight  or 
strongly-marked,  could  be  perpetuated.  The  author  takes  the 
case  of  a  pair  of  animals,  whicli  produce  during  their  lifetime 
two  hundred  offspring,  of  which,  from  various  causes  of  de- 
struction, only  two  on  an  average  survive  to  procreate  their 
kind.  Tliis  is  rather  an  extreme  estimate  for  most  of  the 
higher  animals,  but  by  no  means  so  for  many  of  the  lower 
organisms.  He  then  shows  that  if  a  single  individual  were 
born,  whicli  varied  in  souk*  maimer,  giving  it  twice  as  g'ood  a 
chance  of  life  as  that  of  the  other  individuals,  yet  the  chances 
would  be  strongly  against  its  survival.  Supposing  it  to  sur- 
vive and  to  breed,  and  that  half  its  young  inherited  the  favor- 
able variation  ;  still,  as  the  Reviewer  goes  on  to  show,  the 
young  would  liavo  only  a  slightly-better  chance  of  survaving 


3 1  ILLUSTEATIOKS  OF  TUE  ACTION  OF  Cuap.  IV. 

and  breeding- ;  and  this  chance  would  go  on  decreasing'  in  the 
succeeding  generations.  The  justice  of  these  remarks  cannot, 
I  think,  be  disputed.  If,  for  instance,  a  bird  of  some  kind 
couhl  procure  its  food  more  easily  by  having  its  beak  curved, 
and  if  one  Avere  born  with  its  beak  strongly  carved,  and 
wliich  consequently  flourished,  nevertheless  there  would  be 
a  very  poor  chance  of  this  one  individual  perpetuating  its  kind 
to  the  exclusion  of  the  common  form ;  but  there  can  hardly  be 
a  doubt,  judging  by  what  we  see  taking  place  imder  domesti- 
cation, that  this  result  Avould  follow  from  the  preservation  dur- 
ing many  generations  of  a  large  number  of  indiWduals  with 
more  or  less  curved  beaks,  and  from  the  destruction  of  a  still 
larger  numlier  Avith  the  straightest  beaks. 

It  should  not,  however,  be  overlooked  that  certain  varia- 
tions, which  no  one  would  rank  as  mere  individual  differences, 
frequently  recur,  owing  to  a  similar  organization  being  simi- 
larly acted  on — of  which  fact  numerous  instances  could  be 
given  with  our  domestic  productions.  In  such  cases,  if  a  vary- 
ing individual  did  not  actually  transmit  to  its  offspring  its 
newly-acquired  character,  it  would  imdoubtedly  transmit,  as 
long  as  the  existing  conditions  remained  the  same,  a  still 
stronger  tendency  to  vary  in  the  same  manner.  The  condi- 
tions might  indeed  act  in  so  energetic  and  definite  a  manner  as 
to  lead  to  the  same  modification  in  all  the  individuals  of  the 
species  without  the  aid  of  selection.  But  we  may  suppose 
that  the  conditions  sufficed  to  effect  only  a  third,  or  fourth,  or 
tenth  part  of  the  individuals  ;  and  several  such  cases  could  be 
given ;  for  instance,  it  has  been  estimated  by  Graba  that  in  the 
Faroe  Islands  about  one-fiftli  of  the  guillemots,  Avhich  all  breed 
together,  consist  of  a  well-marked  variety ;  and  this  Avas  for- 
meily  ranked  as  a  distinct  species  under  the  name  of  Uria 
lacrymans.  Now,  in  such  cases,  if  the  variation  were  of  a  ben- 
eficial nature,  the  original  form  would  soon  be  sup})lantcd  by 
the  modified  form,  through  the  survival  of  the  fittest. 

With  reference  to  the  eftects  of  intercrossing  and  of  com- 
petition, it  should  be  borne  in  mind  that  most  animals  antl  plants 
keep  to  their  proper  homes,  and  do  not  needlessly  Avander 
aljout ;  Ave  see  this  CA'cn  Avith  migratory  birds,  Avhich  almost 
always  return  to  the  same  district.  Consequently  each  newly- 
formed  variety  Avould  generally  be  at  lirst  local,  as  seems  to 
1)0  the  common  rule  Avith  A'arieties  in  a  state  of  nature  ;  so  that 
siinilarlA'-modified  individuals  Avould  soon  exist  in  a  small  l)ody 
together,  and  would  often  breed  together.     If  the  v.vw  variety 


Chap.  IV.  NATURAL  SELECTION.  95 

was  successful  in  its  battle  for  life,  it  would  slowly  spread  from 
a  central  spot,  competinp^  Avitli  and  conf[U(>rinof  the  uncluuifred 
individuals  on  the  niar<>-ins  of  an  ever-increasing  circle.  But 
to  the  subject  of  intercrossing  we  shall  have  to  return.  It  may 
be  objected  by  those  who  have  not  attended  to  natural  history, 
that  tlie  long-continued  accumulation  of  individual  differences 
could  not  give  rise  to  parts  or  organs  which  seem  to  us,  and 
arc  often  called,  new.  But,  as  we  shall  hereafter  find,  it  is  dif- 
ficult to  advance  any  good  instance  of  a  really  new  organ  ; 
even  so  complex  and  perfect  an  organ  as  the  eye  can  be  showa  t(< 
graduate  downward  into  mere  tissue  sensitive  to  diffused  light 
It  may  be  worth  Avhile  to  give  another  and  more  complex 
illustration  of  tlie  action  of  natural  selection.  Certain  plants 
excrete  sweet  juice,  apparently  for  the  sake  of  eliminating 
something  injurious  from  their  sap:  this  is  effected,  for  in- 
stance, by  glands  at  the  base  of  the  stipules  in  some  Legunii- 
nosa^,  and  at  the  backs  of  the  leaves  of  the  common  laurel. 
This  juice,  though  small  in  quantity,  is  greedily  sought  by  in- 
sects ;  but  their  visits  do  not  in  any  way  benefit  the  plant. 
Now,  let  us  suppose  that  the  juice  or  nectar  was  excreted 
from  the  inside  of  the  flowers  of  a  certain  number  of  plants  of 
anv  species.  Insects  in  seeking  the  nectar  would  get  dusted 
with  pollen,  and  would  certainly  often  transport  it  from  one 
flower  to  another.  The  flowers  of  two  distinct  individuals  of 
the  same  species  would  thus  get  crossed ;  and  the  act  of  cross- 
ing, as  Ave  have  good  reason  to  believe,  would  produce  vigor- 
ous seedlings,  which  consequently  would  have  the  best  chance 
of  flourishing  and  surviving.  The  plants  which  produced  flow- 
ers with  the  largest  glands  or  nectaries,  excreting  most  nectar, 
would  oftencst  be  visited  by  insects,  and  would  oftenest  be 
crossed  ;  and  so  in  the  long-run  would  gain  the  upper  hand  and 
form  a  local  variet}'.  The  flowers,  also,  wliich  had  their  sta- 
mens and  pistils  placed,  in  relation  to  the  size  and  habits  of  the 
particular  insect  which  visited  them,  so  as  to  favor  in  any 
dcgr(>e  the  transportal  of  the  pollen,  would  likewise  be  favored. 
AVe  might  have  taken  the  case  of  insects  visiting  flowers  for 
Ihc  sake  of  collecting  pollen  instead  of  nectar;  and  as  pollen  is 
formed  for  the  sole  purpose  of  fertilization,  its  destruction  ap- 
pears to  be  a  simple  loss  to  the  plant ;  3-et  if  a  little  pollen 
"were  canied,  at  first  occasionally  and  then  habitually,  by  the 
pollen-devouring  insects  from  flower  to  flower,  and  a  cross  thus 
ellected,  although  nine-tenths  of  the  pollen  were  destroyed,  it 
might  still  be  a  great  gain  to  the  plant;  and   the  individuals 


96  ILLUSTRATIONS  OF  THE  ACTION  OF  Chap.  IV. 

which  produced  more  and  more  pollen,  and  had  larger  anthers, 
would  be  selected. 

"When  our  plant,  by  the  above  process  long  continued,  had 
been  rendered  highly  attractive  to  insects,  they  would,  unin- 
tentionally on  their  part,  regularly  carry  pollen  from  flower  to 
flower;  and  that  they  do  this  cfl'ectually,  I  could  easily  show 
l)y  many  striking  facts.  I  will  give  only  one,  as  likewise  illus- 
trating one  step  in  the  separation  of  the  sexes  of  plants.  Some 
liolly-trees  bear. only  male  flowers,  which  have  four  stamens 
])roducing  a  rather  small  quantity  of  pollen,  and  a  rudimentary 
l)istil ;  other  holly-trees  bear  only  female  flowers ;  these  have 
a  full-sized  pistil,  and  four  stamens  with  shrivelled  anthers,  in 
which  not  a  grain  of  pollen  can  be  detected.  Having  found 
a  female  tree  exactly  sixty  yards  from  a  male  tree,  I  put  the 
stigmas  of  twenty  flowers,  taken  from  difierent  branches,  under 
the  microscope,  and  on  all,  without  exception,  there  were  a  few 
pollen-grains,  and  on  some  a  profusion.  As  the  wind  had  set 
for  several  days  from  the  female  to  the  male  tree,  the  pollen 
could  not  thus  have  been  carried.  The  weather  had  been  cold 
and  boisterous,  and  therefore  not  favorable  to  bees,  neverthe- 
less every  female  flower  which  I  examined  had  been  effectually 
fertilized  by  the  bees,  which  had  flown  from  tree  to  tree  in 
search  of  nectar.  But  to  return  to  our  imaginary  case :  as 
soon  as  the  plant  had  been  rendered  so  highly  attractive  to 
insects  that  pollen  was  regularly  carried  from  flower  to  flower, 
another  process  might  commence.  No  naturalist  doubts  the 
advantage  of  what  has  been  called  the  "  physiological  division 
of  labor ; "  hence  we  may  believe  that  it  would  be  advanta- 
geous to  a  plant  to  produce  stamens  alone  in  one  flower  or  on 
one  whole  plant,  and  pistils  alone  in  another  flower  or  on 
another  plant.  In  plants  under  culture  and  placed  under  new 
conditions  of  life,  sometimes  the  male  organs  and  sometimes 
the  female  organs  become  more  or  less  impotent ;  now  if  we 
suppose  this  to  occur  in  ever  so  slight  a  degree  under  Nature, 
tlien,  as  pollen  is  already  carried  regularly  from  flower  to  flower, 
and  as  a  more  complete  separation  of  the  sexes  of  our  plant 
would  be  advantageous  on  the  principle  of  the  di\'ision  of 
labor,  individuals  with  this  tendency  more  and  more  increased, 
would  be  continually  favored  or  selected,  until  at  last  a  eoin- 
phite  separation  of  the  sexes  might  be  effected.  It  would 
take  up  too  much  space  to  show  the  various  steps,  through 
diinorpliism  and  other  means,  by  which  the  separation  of  the 
sexes  in  plants  of  various  kinds  is  aiiparently  now  in  progress ; 


Chap.  IV.  NATUKAL  SELECTION.  97 

but  I  may  add  that  .some  of  the  species  of  holly  in  North 
America  are,  accordiiifj  to  Asa  Gray,  in  an  intermediate  con- 
dition, or,  as  he  cxpixvsses  it,  arc  more  or  less  diceciously  po- 
lygamous. 

Let  us  now  turn  to  the  nectar-feeding  insects.  We  may 
suppose  the  plant,  of  which  we  have  been  slowly  increasing 
the  nectar  hy  continued  selection,  to  be  a  common  plant ;  and 
that  certain  insects  depended  in  main  part  on  its  nectar  for 
fooil.  I  could  give  many  facts,  showing  how  anxious  bees  are 
to  save  time:  for  instance,  their  habit  of  cutting  holes  and 
sucking  the  nectar  at  the  bases  of  certain  flowers,  which  they 
can,  with  a  very  little  more  troul)le,  enter  by  the  mouth. 
Bearing  such  facts  in  mind,  it  may  be  believed  that,  under  cer- 
tain circumstances,  individual  differences  in  the  curvature  or 
length  of  the  proboscis,  etc.,  too  slight  to  be  appreciated  by 
us,  might  profit  a  bee  or  other  insect,  so  that  certain  individ- 
uals would  be  able  to  obtain  their  food  more  quickly  than 
others ;  and  thus  the  communities  to  which  they  belonged 
would  ilourish  and  throw  off  many  swarms  inheriting  the  same 
peculiarities.  The  tulles  of  the  corolla  of  the  common  red  and 
incarnate  clovers  (Trifolium  pratense  and  incarnatum)  do  not 
on  a  hasty  glance  appear  to  differ  in  length ;  yet  the  hive-bee 
ran  easily  suck  the  nectar  out  of  the  incarnate  clover,  but  not 
out  of  the  common  red  clover,  Avhich  is  visited  by  humble-bees 
alone ;  so  that  whole  fields  of  the  red  clover  in  vain  offer  an 
abundant  supply  of  precious  nectar  to  the  hive-bee.  Tliat  this 
nectar  is  much  liked  by  the  hive-bee  is  certain ;  for  I  have  re- 
])eatedly  seen,  but  only  in  the  autumn,  many  hive-bees  sucking 
the  (lowei-s  through  holes  bitten  in  the  base  of  the  tube  by 
humble-bees.  The  difference  in  the  length  of  the  corolla  in 
the  two  kinds  of  clover,  which  determines  the  visits  of  the 
hive-bee,  must  be  very  trifling ;  for  I  have  been  assured  that 
when  red  clover  has  been  mown,  the  flowers  of  the  second  crop 
nve  somewhat  smaller,  and  that  these  are  visited  by  many 
hive-bees.  I  do  not  know  whether  this  statement  is  accurate; 
nor  whether  another  published  statement  can  be  trusted,  namely, 
that  the  Ligurian  bee,  which  is  generally  considered  a  mere 
variety  and  which  freely  crosses  with  the  common  hive-bee,  is 
able  to.  reach  and  suck  the  nectar  of  the  connnon  red  clover. 
Thus,  in  a  country  where  this  kind  of  clover  abounded,  it  might 
be  a  great  advantage  to  the  hive-bee  to  have  a  slightly-longer 
or  differently-constructed  proboscis..  On  the  other  hand,  as 
the  fertility  of  this  clover  absolutely  depends  on  bees  visiting 


98  INTEECEOSSING   OF  INDIVIDUALS.  Chap.  IV. 

tlio  llowiTri,  if  humble-bees  were  to  become  rare  in  any  country, 
it  miglit  be  a  great  advantage  to  the  plant  to  have  a  shorter 
or  more  deeply-divided  corolhi,  so  that  the  hive-bees  should  be 
induced  to  suck  its  flowers.  Thus  I  can  understand  how  a 
flower  and  a  bee  might  slowly  become,  either  simultaneously 
or  one  after  the  other,  modified  and  adapted  to  each  other  in 
the  most  perfect  manner,  by  the  continued  preservation  of  all 
the  individuals  M'hich  presented  slight  deviations  of  structure 
mutually  favorable  to  each  other. 

I  am  Avcll  aware  that  this  doctrine  of  natural  selection, 
exemplified  in  the  above  imaginary  instances,  is  open  to  the 
same  objections  which  were  at  first  urged  against  Sir  Charles 
Lycll's  noble  \aews  on  "  the  modern  changes  of  the  earth,  as 
illustrative  of  geology ; "  but  Ave  now  seldom  hear  the  agencies, 
still  at  work,  spoken  of  as  trifling  or  insignificant,  when  applied 
to  the  excavation  of  the  deepest  valleys  or  to  the  formation  of 
long  lines  of  inland  cliffs.  Natural  selection  acts  only  by  the 
preservation  and  accumulation  of  small  inherited  modifications, 
each  profitable  to  the  preserved  being ;  and  as  modern  geology- 
has  almost  banished  such  views  as  the  excavation  of  a  great 
valley  by  a  single  diluvial  wave,  so  will  natural  selection,  if 
it  be  a  true  principle,  banish  the  belief  of  the  continued  crea- 
tion of  new  organic  beings,  or  of  any  great  and  sudden  modifi- 
cation in  their  structure. 

On  the  Infererossmff  of  Individuals. 

I  must  here  introduce  a  short  digression.  In  the  case  of 
animals  and  plants  with  separated  sexes,  it  is  of  course  obvi- 
ous that  two  individuals  must  always  (with  the  exception  of 
the  curious  and  not  well-understood  cases  of  parthenogenesis) 
unite  for  each  birth  ;  but  in  the  case  of  hermaphrodites  this  is 
far  from  obvious.  Nevertheless  tliere  is  reason  to  believe  that 
with  all  hermaphrodites  two  individuals,  either  occasionally  or 
habitually,  concur  for  the  reproduction  of  their  kind.  This 
vicAV  was  first  suggested  by  Andrew  Knight.  "SVe  shall  pres- 
enth'  see  its  importance :  but  I  must  here  treat  the  subject 
with  extreme  1)revity,  thougli  I  have  the  materials  prepared 
for  an  anijile  discussion.  All  vertebrate  animals,  all  insects, 
and  some  other  large  groups  of  animals,  pair  for  each  birth. 
Modern  research  has  nuich  diminished  the  number  of  supjiosed 
hermajihrodites,  and  of  real  hermaphrodites  a  large  number 
pair;   that  is,  two  individuals  regularly  unite  for  reproduction, 


CiiAr.  IV.  INTERCROSSING  OF  INDIVIDUALS.  99 

Aviiieh  is  all  that  concerns  us.  But  still  there  arc  many  lier- 
maphrodito  animals  wliicli  certainly  do  not  habitually  pair,  and 
a  \-ast  majority  of  plants  are  hermaphrodites.  What  reason,  it 
may  be  asked,  is  there  for  supposing  in  these  cases  that  two 
individuals  ever  concur  in  reproduction?  As  it  is  impossible 
here  to  enter  on  details,  I  nuist  trust  to  some  general  consid- 
erations alone. 

In  the  first  place,  I  have  collected  so  large  a  body  of  facts, 
showing,  in  accordance  with  the  almost  universal  belief  of 
breeders,  that  Avith  animals  and  plants  a  cross  between  differ- 
ent varieties,  or  between  individuals  of  the  same  variety  but 
of  another  strain,  gives  vigor  and  fertility  to  the  offspring ; 
and  on  the  other  hand,  that  dose  interbreeding  diminishes  vig- 
or and  fertility  ;  tliat  these  facts  alone  incline  me  to  believe 
that  it  is  a  general  law  of  Nature  that  no  organic  being  fertil- 
izes itself  for  a  perpetuity  of  generations ;  but  that  a  cross 
with  another  individual  is  occasionally — perhaps  at  long  inter- 
vals of  time — indispensable. 

On  the  belief  that  this  is  a  law  of  Nature,  we  can,  I  think, 
miderstand  several  large  classes  of  facts,  such  as  the  follow- 
ing, which  on  any  other  view  are  inexplicable.  Every  hybrid- 
izer knows  how  unfavorable  exposure  to  wet  is  to  the  fertili- 
zation of  a  flower,  yet  Avhat  a  multitude  of  flowers  have  their 
anthers  and  stigmas  fully  exposed  to  the  weather !  If  an 
occasional  cross  be  indispensable,  notwithstanding  that  the 
plant's  own  anthers  and  pistil  stand  so  near  each  other  as 
almost  to  insure  self-fertilization,  the  fullest  freedom  for  the 
entrance  of  pollen  from  another  individual  Avill  explain  the 
above  state  of  exposure  of  the  organs.  Many  flowers,  on  the 
other  hand,  have  their  organs  of  fructification  closely  enclosed, 
as  in  the  great  papilionaceous  or  pea-fainily ;  but  in  most  of 
these  flowers  there  is  a  curious  adaptation  between  their  struc- 
ture and  the  manner  in  which  bees  suck  the  nectar;  for,  in 
doing  this,  they  either  push  the  flower's  own  pollen  on  the 
stigma,  or  bring  pollen  from  another  flower.  So  necessary  are 
the  visits  of  bees  to  many  ]iapiIionaceous  flowers,  that  I  have 
found,  by  experiments  published  elsewhere,  that  their  fertility 
is  greatly  diminished  if  these  visits  be  prevented.  Now,  it  is 
scarcely  possible  that  bees  should  fly  from  flower  to  flower, 
and  not  carry  pollen  from  one  to  the  other,  to  the  great  good, 
as  I  believe,  of  the  plant.  IJees  will  act  lik(^  a  camel-hair  pen- 
cil, and  it  is  quite  sufficient  just  to  touch  the  anthers  of  one 
flower  and  then  the  stigma  of  another  with  the  same  brush  to 


100  INTEKCEOSSING  OF  INDIVIDUALS.  Ca.vp.  IV. 

insure  fertilization ;  but  it  must  not  be  supposed  that  bees 
would  thus  produce  a  multitude  of  hybrids  between  distinct 
species ;  for  if  you  brinf^  on  the  same  brush  a  plant's  own  pol- 
len and  pollen  from  another  species,  the  former  will  have  such 
a  prepotent  effect,  that  it  will  invariably  and  completely  de- 
stroy, as  has  been  shown  by  Gartner,  any  influence  from  the 
foreig'n  pollen, 

^V'hen  the  stamens  of  a  flower  suddenly  spring  toward  the 
pistil,  or  slowly  move  one  after  the  other  toward  it,  the  con- 
trivance seems  adapted  solely  to  insure  self-fertilization ;  and 
no  doubt  it  is  useful  for  this  end :  but  the  agency  of  insects  is 
often  required  to  cause  the  stamens  to  spring  forward,  as  Kol- 
reutcr  has  shown  to  be  the  case  with  the  barberry ;  and  in  this 
very  genus,  which  seems  to  have  a  special  contrivance  for  self- 
fertilization,  it  is  well  known  that,  if  closely-allied  forms  or 
varieties  are  planted  near  each  other,  it  is  hardly  possible  to 
raise  pure  seedlings,  so  largely  do  they  naturally  cross.  In 
many  other  cases,  far  from  there  being  any  aids  for  self-fertili- 
zation, there  are  special  contrivances,  as  I  could  show  from  the 
writings  of  C  C.  Sprengel  and  from  my  own  observations, 
which  effectually  prevent  the  stigma  receiving  pollen  from  its 
own  flower :  for  instance,  in  Lobelia  fulgens,  there  is  a  really 
beautiful  and  elaborate  contrivance  by  which  all  the  infinitely 
numerous  pollen-granules  are  swept  out  of  the  conjoined  an- 
thers of  each  flower,  before  the  stigma  of  that  individual  flower 
is  ready  to  receive  them;  and  as  this  flower  is  never  visited,  at 
least  in  my  garden,  b}^  insects,  it  never  sets  a  seed,  though  by 
placing  pollen  from  one  flower  on  the  stigma  of  another,  I 
raised  plenty  of  seedlings  ;  and  while  another  species  of  Lobe- 
lia growing  close  by,  which  is  visited  by  bees,  seeds  freely. 
In  very  many  other  cases,  though  there  be  no  special  mechani- 
cal contrivance  to  prevent  the  stigma  of  a  flower  receiving  its 
own  pollen,  yet,  as  C.  C.  Sprengel  has  shown,  and  as  I  can 
confirm,  either  the  anthers  burst  before  the  stigma  is  ready  for 
fertilization,  or  the  stigma  is  ready  before  the  pollen  of  that 
flower  is  ready,  so  tliat  these  plants  have  in  fact  separated 
sexes,  and  nnist  habitually  be  crossed.  So  it  is  with  the  recip- 
rocally dimorphic  and  trimorphic  plants  pre\dously  alluded  to. 
How  strange  are  these  facts !  How  strange  that  the  pollen 
and  stigmatic  surface  of  the  same  flower,  though  placed  so 
close  together,  as  if  for  the  very  purpose  of  self-fertilization, 
should  in  so  many  cases  be  nuitually  useless  to  each  other! 
Hov>'  simjily  are  these  facts    explained  on  the  view  of  an  oeca- 


OiAP.  IV.  INTERCROSSING  OF  INDIVIDUALS.  101 

sional  cross  Avilli  a  distinct  individual  being  advantageous  or 
indispensable  ! 

If  several  varieties  of  tlie  cabbage,  radish,  onion,  and  of 
some  otlicr  plants,  be  allowed  to  seed  near  eacli  other,  a  large 
majority,  as  I  have  found,  of  the  seedlings  thus  raised  will 
turn  out  mongrels  :  for  instance,  I  raised  233  seedling  cab- 
Ixigcs  from  some  jilants  of  different  varieties  growing  near 
each  other,  and  of  these  only  78  were  true  to  their  kind,  and 
some  even  of  these  were  not  perfectly  true.  Yet  the  pistil  of 
each  cabbage-flower  is  surrounded  not  only  l)y  its  own  six  sta- 
mens, but  by  those  of  the  many  other  flowers  on  the  same  plant; 
and  the  pollen  of  each  flower  readily  gets  on  its  own  stigma 
without  insect-agency  ;  for  I  have  found  that  a  plant  carefully 
protected  produced  the  full  number  of  pods.  How,  then, 
comes  it  that  sucli  a  vast  number  of  the  seedlings  are  mongrel- 
ized  ?  •  I  suspect  that  it  must  arise  from  the  pollen  of  a  distinct 
varii'tj/  having  a  prepotent  effect  over  a  flower's  own  pollen  ; 
and  that  this  is  part  of  the  general  law  of  good  being  derived 
from  the  intercrossing  of  distinct  individuals  of  the  same  spe- 
cies. When  distinct  species  are  crossed  the  case  is  directly  the 
reverse,  for  a  jilant's  own  pollen  is  almost  always  prepotent 
over  foreign  pollen  ;  but  to  this  subject  Ave  shall  return  in  a 
future  chapter. 

In  the  case  of  a  large  tree  covered  with  innumerable  flow- 
ers, it  may  be  objected  that  pollen  could  seldom  be  carried 
from  tree  to  tree,  and  at  most  only  from  flower  to  flower  on 
the  same  tre*,  and  that  flowers  on  the  same  tree  can  be  con- 
sidered as  distinct  individuals  only  in  a  limited  sense.  I  be- 
lieve this  objection  to  be  valid,  but  that  Nature  has  largely  pro- 
vided against  it  by  giving  to  trees  a  strong  tendency  to  bear 
flowers  with  separated  sexes.  When  the  sexes  are  separated, 
although  the  male  and  female  flowers  may  be  produced  on  the 
same  tree,  we  can  see  that  pollen  must  be  regularly  carried 
from  flower  to  flower;  and  this  will  give  a  better  chance  of 
]i()llen  being  occasionally  carried  from  tree  to  tree.  That  trees 
belonging  to  all  Ord<»rs  have  their  sexes  more  often  separated 
than  other  plants,  I  And  to  be  the  case  in  this  country  ;  and  at 
my  request  Dr.  Hooker  tabulated  the  trees  of  New  Zealand, 
and  Dr.  Asa  Gray  those  of  the  United  States,  and  the  result 
was  as  I  anticipated.  On  the  other  hand.  Dr.  Hooker  has  re- 
cently informc(l  me  that  he  flnds  that  the  rule  does  not  hold  in 
Australia ;  and  I  have  made  these  few  remarks  on  the  sexes  of 
trees  simply  to  call  attention  to  the  subject. 


102  INTERCROSSING  OF  INDIVIDUALS.  Cii\r.  IV. 

Turning-  for  a  very  brief  space  to  animals  :  on  ilic  land 
there  are  some  hcrmaplirodites,  as  land-moUusca  and  eartli- 
worms  ;  but  these  all  pair.  As  yet  I  have  not  found  a  single 
case  of  a  terrestrial  animal  Avhich  fertilizes  itself.  Wc  can  un- 
derstand this  remarkable  fact,  Avhich  offers  so  strong  a  contrast 
Avith  terrestrial  plants,  on  the  view  of  an  occasional  cross  being 
indispensable,  by  considering  the  medium  in  which  terrestrial 
animals  live,  and  the  nature  of  the  fertilizing  element ;  for  we 
know  of  no  means,  analogous  to  the  action  of  insects  and  of 
the  wind  in  the  case  of  plants,  by  which  an  occasional  cross 
could  be  effected  "with  terrestrial  animals,  "without  the  concur- 
rence of  two  individuals.  Of  aquatic  animals,  there  are  many 
self-fertilizing  hermaphrodites ;  but  here  currents  in  the  water 
offer  an  obvious  means  for  an  occasional  cross.  And,  as  in  the 
case  of  flowers,  I  have  as  yet  failed,  after  consultation  Avith 
one  of  the  highest  authorities,  namely,  Prof.  Huxley,  to  dis- 
cover a  single  case  of  an  hermaphrodite  anim:il  with  the  organs 
of  reproduction  so  perfectly  enclosed  within  the  body,  that  ac- 
cess from  without  and  the  occasional  influence  of  a  distinct  in- 
dividual can  be  shown  to  be  physically  impossible.  Cirripedes 
long  appeared  to  me  to  present  a  case  of  very  great  difficulty 
under  this  point  of  view ;  but  I  have  been  enabled,  by  a 
fortunate  chance,  elsewhere  to  prove  that  two  individuals, 
though  both  are  self-fertilizing  hermaphrodites,  do  sonietimcs 
cross. 

It  must  have  struck  most  naturalists  as  a  strange  anomaly 
that,  in  the  case  of  both  animals  and  plants,  species  of  the  same 
family  and  even  of  the  same  genus,  though  agreeing  closely 
with  each  other  in  almost  their  whole  organization,  yet  are  not 
rarely,  some  of  them  hermaphrodites,  and  some  of  them  uni- 
sexual. But  if,  in  fact,  all  hermaphrodites  do  occasionally  in- 
tercross with  other  individuals,  the  difference  between  hermaph- 
rodites and  unisexual  species,  as  far  as  function  is  concerned, 
becomes  very  small. 

From  these  several  considerations  and  from  the  many  spe- 
cial facts  which  I  have  collected,  but  which  I  am  not  here  able 
to  give,  I  am  strongly  inclined  to  suspect  that,  both  in  the 
vegetable  and  animal  kingdoms,  an  occasional  intercross  with 
a  distinct  individual  is  a  law  of  Nature.  I  am  well  aware  that 
there  are,  on  this  view,  many  cases  of  difficulty,  some  of  which 
I  am  trying  to  investigate.  Finally,  then,  we  may  conclude 
that,  in  many  organic  beings,  a  cross  between  two  individuals 
is  an  ()l)vious  necessity  for  each  l)irth ;  in  many  others  it  occurs 


Chai-.  IV.  niODUCTION  OF  NEW  FORMS.  103 

perhaps  only  at  long'  intervals  ;  but  in  none,  as  I  suspect,  can 
self-fertilization  go  on  for  perpetuity. 

Clrcnmstanccs  favorable  for  the  Production  of  Neio  Forms 
through  Natural  Selection. 

Tliis  is  an  extremely  intricate  subject.  A  great  amount  of 
variability,  under  which  term  individual  differences  are  always 
included,  will  evidently  be  favorable.  A  large  number  of  in- 
dividuals, by  giving  a  better  chance  for  the  appearance  of 
profitable  variations  within  any  given  period,  will  compensate 
for  a  lesser  amount  of  variability  in  each  individual,  and  is,  I 
believe,  an  extremely  important  element  of  success.  Though 
Nature  grants  long  periods  of  time  for  the  work  of  natural  se- 
lection, she  does  not  grant  an  indefinite  period ;  for,  as  all  or- 
ganic -beings  arc  striving  to  seize  on  each  place  in  the  economy 
of  Nature,  if  any  one  species  docs  not  become  modified  and  im- 
proved in  a  corresponding  degree  with  its  competitors,  it  will 
be  exterminated.  Unless  favorable  variations  be  inherited  by 
some  at  least  of  the  offspring,  nothing  can  be  effected  by  nat- 
ural sclecticjn.  Tlie  tendency  to  reversion  may.  often  check  or 
prevent  the  work  ;  but  as  tliis  tendency  has  not  prevented 
man  from  forming  by  selection  nimierous  domestic  races,  why 
.sliould  it  prevail  against  natural  selection  ? 

In  the  case  of  methodical  selection,  a  breeder  selects  for 
some  definite  object,  and  free  intercrossing  Avill  wholly  stop 
his  work.  But  when  many  men,  without  intending  to  alter  the 
breed,  have  a  nearly  common  standard  of  perfection,  and  all 
try  to  procure  and  breed  from  the  best  animals,  much  improve- 
ment surely  but  slowly  follows  from  this  unconscious  process 
of  selection,  notwithstanding  a  large  amount  of  crossing  with 
inferior  animals.  Thus  it  Avill  be  in  Nature;  for  within  a  con- 
Ihied  area,  with  some  place  in  its  polity  not  perfectly  occu]iicd, 
natural  selection  will  always  tend  to  preserve  all  the  individ- 
uals varying  in  the  right  direction,  though  in  different  degrees, 
so  as  better  to  fill  up  the  imoccupied  place.  But  if  the  area  be 
very  large,  its  several  districts  will  almost  certainly  present 
different  conditions  of  life  ;  and  then,  if  the  same  species  under- 
g()(^s  modification  in  different  parts,  the  newly-formed  varieties 
will  intercross  on  the  confines  of  each  district.  But  we  shall 
see  in  the  seventh  chapter  that  intermediate  varieties,  inhabit- 
ing an  intermediate  district,  whether  the  result  of  the  crossing 
of  other  varieties,  or  originally  formed  with  an  intermediate 


104  CIRCUMSTANCES  TAYOKABLE  TO  THE         CnAr.  IV. 

character,  will  in  llie  lonrr-run  generally  be  supplanted  by  one 
of  the  varieties  on  either  hand.  Intercrossing  will  aflect  those 
animals  most  which  unite  for  each  birth  and  Avauder  much,  and 
which  do  not  breed  at  a  very  quick  rate.  Hence  with  animals 
of  this  nature,  for  instance  birds,  varieties  will  generally  be 
confined  to  separated  countries  ;  and  this  I  find  to  be  the  case. 
With  hennaphrodite  organisms  which  cross  only  occasionally, 
and  likewise  with  animals  which  unite  for  each  l)irth,but  which 
wander  little  and  can  increase  at  a  very  rapid  rate,  a  new  and 
iinpro\'ed  variety  might  be  quickly  formed  on  any  one  spot, 
and  might  there  maintain  itself  in  a  body  and  afterward 
spread,  so  that  the  crossing  would  be  chiefly  between  the  indi- 
viduals of  the  new  variety  living  together  in  the  same  place. 
On  this  principle,  nurserymen  always  prefer  saving  seed  from 
a  large  body  of  plants,  as  the  chance  of  intercrossing  is  thus 
lessened. 

Even  in  the  case  of  animals  which  breed  slowly  and  xmite 
for  each  birtli,  Ave  must  not  assume  that  the  effects  of  natural 
selection  Avill  always  be  immediately  oveq:)OAvered  by  free  inter- 
crossing ;  for  I  can  bring  a  considerable  body  of  facts,  showing 
that,  Avitljin  the- same  area,  varieties  of  the  same  animal  may 
long  remain  distinct,  from  haunting  different  stations,  from 
breeding  at  slightly-tlifferent  seasons,  or  from  varieties  of  the 
same  kind  preferring  to  pair  together. 

Intercrossing  plays  a  very  important  part  in  Nature  in  keep- 
ing the  individuals  of  the  same  species,  or  of  the  same  \'ariety, 
true  and  xmifonn  in  character.  It  will  obviously  thus  act  far 
more  elViciently  with  those  animals  Avhich  unite  for  each  birth ; 
but  as  already  stated  we  have  reason  to  believe  that  occasional 
intercrosses  take  place  with  all  animals  and  with  all  plants. 
Even  if  these  take  ]ilace  only  at  long  intcr\-als  of  time,  the 
young  thus  produced  Avill  gain  so  much  in  vigor  and  fertihty 
over  the  offspring  from  long-continued  self-fertilization,  that 
the}'  Avill  have  a  better  chance  of  surviving  and  propagat- 
ing their  kind  ;  and  thus,  in  the  long-run,  the  influence  of  inter- 
crosses, even  at  rare  intervals,  will  be  great.  If  there  exist 
organic  beings  which  never  intercross,  uniformity  of  character 
ran  be  retained  among  them,  as  long  as  their  conditions  of 
life  remain  tho  same,  only  through  the  principle  of  inheritance 
and  through  natural  selection  destroying  any  which  depart  from 
tlic  proper  type  ;  but  if  their  conditions  of  life  change  and  they 
undergo  modification,  xmiformity  of  character  can  be  given  to 
their  modified  offspring,  solely  b^'  natural  selection  prescn-ing 
similar  favorable  variations. 


Cbap.  IV.  KESULTS  OF  NATURAL  SELECTION.  IQH 

Isolation,  also,  is  an  important  clement  in  the  changes 
effected  tlirout^h  natural  selection.  In  a  confined  or  isolated 
area,  if  not  very  large,  the  organic  and  inorganic  conditions  of 
life  will  generally  be  almost  uniform ;  so  that  natural  selection 
will  tend  to  modify  all  the  varying  individuals  of  the  same  spe- 
cies in  the  same  manner.  Intercrossing  with  the  inhal)itants 
of  the  surrounding  districts  ^vill,  also,  be  prevented.  Moritz 
Wagner  has  lately  published  an  interesting  essay  on  this  sub- 
ject, and  has  shown  that  the  service  rendered  by  isolation  in 
preventing  crosses  between  newly-formed  varieties  is  probably 
greater  even  than  I  have  supposed.  But  from  reasons  already 
assigned  I  can  by  no  means  agree  with  this  naturalist,  that 
migration  and  isolation  are  necessary  for  the  formation  of  new 
species.  The  importance  of  isolation  is  likewise  great  in  pre- 
venting, after  any  physical  change  in  the  conditions,  such  as  of 
climate,  elevation  of  the  land,  etc.,  the  immigration  of  better- 
adapted  organisms ;  and  thus  new  places  in  the  natural  econ- 
cmy  of  the  district  are  left  open  for  the  old  inhabitants  to  strug- 
gle for  and  become  ada])ted  to.  Lastly,  isolation  will  give  time 
for  a  new  variety  to  be  slowly  improved ;  and  this  may  some- 
times be  of  importance  in  the  productioTi  of  new  species.  If, 
however,  an  isolated  area  be  very  small,  either  from  being  sur- 
rounded by  jjarriers,  or  from  having  very  peculiar  physical  con- 
ditions, the  total  number  of  the  inlialiitants  will  be  small ;  and 
this  will  retard  the  production  of  new  species  through  natural 
selection,  by  decreasing  the  chances  of  the  appearance  of  favor- 
able individual  diflerences. 

The  mere  lapse  of  time  by  itself  does  nothing  either  for  or 
against  natural  selection.  I  state  this  because  it  has  been 
erroneously  asserted  that  the  element  of  time  has  been  assumed 
by  me  to  play  an  all-imjiortant  part  in  modifying  species,  as  if 
all  ^vere  necessarily  undergoing  change  through  the  action  of 
some  iimate  law.  Lapse  of  time  is  only  so  fur  injportant,  and 
its  importance  in  this  respect  is  great,  that  it  gives  a  better 
chaiKMj  of  beneficial  variations  arising,  being  selected,  increased, 
and  fixed,  in  relation  to  the;  slowly-clianging  organic  and  in- 
organic (•f)iiditions  of  life.  It  likewise  favors  the  definite  action 
of  the  conditions  of  life. 

If  \\c  turn  to  Nature  to  test  the  truth  of  these  remarks,  and 
look  at  any  small,  isolated  area,  such  as  an  oceanic  island,  al- 
though the  number  of  the  dilTt^rent  species  inhabiting  it  is  small, 
as  we  shall  see  in  our  chapter  on  Geographical  Distribution; 
yet  of  the  species  a  very  large  proportion  are  endemic — that  is, 


lOO  CinCU.MSTANCES  FAVORABLE  TO  THE         Ciiap.  IV, 

have  l.ccn  produced  llicre,  and  nowhere  else  in  the  world. 
Hencn^  :m  oceanic  ishxnd  at  first  sie^ht  seems  to  have  been 
hig'hly  favorable  for  the  production  of  new  species.  But  we 
may  thus  deceive  ourselves,  for,  to  ascertain  whether  a  small, 
isolated  area,  or  a  large  open  area  like  a  continent,  has  been 
most  favorable  for  the  production  of  new  organic  forms,  we 
ought  to  make  the  comparison  -within  equal  times ;  and  this 
wc  are  incajiahlo  of  doing. 

Although  isolation  is  of  great  importance  in  the  production 
of  new  species,  on  the  Avhole  I  am  inclined  to  believe  that  large- 
ness of  area  is  still  more  important,  especially  for  the  produc- 
tion of  species  which  shall  prove  capable  of  enduring  for  a  long 
period,  and  of  spreading  Avidcly.  Throughout  a  great  and  open 
area,  not  only  Avill  there  be  a  better  chance  of  favorable  varia- 
tions arising  from  the  large  number  of  individuals  of  the  same 
species  there  supported,  but  the  conditions  of  life  are  much 
more  complex  from  the  large  number  of  already  existing  spe- 
cies ;  and  if  some  of  these  many  species  become  modified  and 
improved,  others  will  have  to  be  improved  in  a  corresponding 
degree,  or  they  will  be  exterminated.  Each  new  form,  also,  as 
soon  as  it  has  been  much  improved,  will  be  able  to  spread  over 
the  open  and  continuous  area,  and  will  thus  come  into  compe- 
tition with  many  others.  Moreover,  great  areas,  though  now 
continuous,  owing  to  former  oscillations  of  level,  will  often 
have  existed  in  a  broken  condition,  so  that  the  good  effects  of 
isolation  will  generally,  to  a  certain  extent,  have  concuiTed. 
Finally,  I  conclude  that,  although  small  isolated  areas  probably 
have  beeii  in  some  respects  highly  favorable  for  the  production 
of  new  species,  yet  that  the  course  of  modification  will  gener- 
ally have  been  more  rapid  on  large  areas ;  and,  what  is  more 
important,  that  the  new  forms  j)roduced  on  large  areas,  which 
already  have  been  victorious  over  many  competitors,  will  be 
tliose  that  will  s])rea(l  most  widely,  will  give  rise  to  most  new 
varit^ties  and  species,  and  will  thus  play  the  most  important 
part  in  the  changing  history  of  the  organic  Avorld. 

We  can,  perhaps,  on  these  Aiews,  imderstand  some  facts 
wliich  will  be  again  alluded  to  in  our  chapter  on  Geographical 
Distribution  ;  for  instance,  that  the  ]iroductions  of  the  smaller 
continent  of  Australia  are  now  yielding  before  those  of  the 
larger  Europa'o- Asiatic  area.  Thus,  also,  it  is  that  continental 
pniductions  have  everywhere  become  so  largely  naturalized  on 
islands.  On  a  small  island,  the  race  for  life  will  have  been  less 
severe,  and  there  will  have  been  less  modification  and  less  ex- 


Chap.  IV.  KESULTS  OF  NATURAL  SELECTION.  iQ>j 

termination.  Ilcncc,  perhaps,  it  is  liiat  the  flora  of  Madeira, 
accordin<^  to  Oswald  Heer,  resembles  the  extinct  tertiary  flora 
of  Europe.  ^Vll  fresh-water  basins,  taken  together,  make  a 
small  area  compared  with  that  of  the  sea  or  of  the  land  ;  and, 
consequently,  the  competition  between  fresh-water  productions 
will  have  been  less  severe  than  elsewhere  ;  new  forms  will  have 
been  more  slowly  formed,  and  old  forms  more  slowly  extermi- 
nated. And  it  is  in  fresh  water  that  Ave  find  seven  genera  of 
Ganoid  fishes,  remnants  of  a  once  preponderant  order :  and  in 
ii?sh  water  we  find  some  of  the  most  anomalous  forms  now 
known  in  the  world,  as  the  Ornithorhynchus  and  Lepidosiren, 
which,  like  fossils,  connect  to  a  certain  extent  orders  at  present 
widely  separated  in  the  natural  scale.  These  anomalous  forms 
may  be  called  living  fossils ;  they  have  endured  to  the  present 
day,  from  having  inhabited  a  confined  area,  and  having  been 
exposed  to  less  varied  and  therefore  less  severe  competition. 

To  sum  up  the  circumstances  favorable  and  unfavorable  for 
the  production  of  new  species  through  natural  selection,  as  far 
as  the  extreme  intricacy  of  the  svibject  permits.  I  conclude 
that  fur  terrestrial  productions  a  large  continental  area,  which 
has  imdergone  many  oscillations  of  level,  will  have  been  the 
most  favorable  for  the  production  of  many  ncAV  forms  of  life, 
fitted  to  endure  for  a  long  time  and  to  spread  widely.  While 
the  area  existed  as  a  continent,  the  inhabitants  will  have  been 
numerous  in  individuals  and  kinds,  and  Avill  have  been  subjected 
to  severe  competition.  When  converted  by  subsidence  into 
large  separate  islands,  there  will  still  have  existed  many  indi- 
viduals of  the  same  species  on  each  island:  intercrossing  on  the 
confines  of  the  range  of  each  new  species  will  have  been 
checked :  after  physical  changes  of  any  kind,  immigration  will 
have  been  prevented,  so  that  new  places  in  the  polity  of  each 
island  will  have  had  to  be  filled  up  by  modifications  of  the  old 
inhabitants;  and  time  will  have  been  allowed  for  the  varieties 
in  each  to  become  well  modified  and  perfected.  When,  by 
renewed  elevation,  the  islands  were  reconverted  into  a  conti- 
nental area,  there  will  again  have  been  severe  competition  : 
the  most  faxorcd  or  improved  varieties  will  have  been  enabled 
to  spread  :  there  will  have  been  much  extinction  of  the  less 
improved  forms,  and  the  relative  proportional  ninnbcrs  of  the 
various  inhabitants  of  tin;  reunited  continent  will  again  have 
been  changed ;  and,  again,  there  will  have  been  a  fair  lield  for 
natural  selection  to  improve  still  further  the  inhabitants,  and 
thus  to  produce  new  species. 


108  EXTIXCTIOX  BY  NATURAL  SELECTION.       CiiAP.  IV. 

That  natural  sc^lcction  acts  "vvith  extreme  slowness  I  fully 
iidniit.  The  result  depends  on  there  beings  places  in  the  polity 
of  Nature,  wliich  can  be  better  filled  through  some  of  the  in- 
habitants of  the  country  undergoinf^  modifications  of  some  kind. 
The  existence  of  such  places  will  often  depend  on  physical 
changes,  which  are  generally  very  slow,  and  on  the  immigra- 
tion of  better-adapted  forms  being  checked.  But  the  effects 
of  natural  selection  will  probably  still  oftener  depend  on  some 
few  of  the  inhabitants  becoming  slowly  modified  ;  the  mutual 
relations  of  the  other  inhabitants  being  thus  disturbed.  Al- 
though all  the  individuals  of  the  same  species  differ  more  or 
less  from  each  other,  differences  of  the  right  nature,  better 
adapted  to  the  then  existing  conditions,  may  not  soon  occur. 
The  results  will  often  be  greatly  retarded  by  free  intercrossing. 
Many  will  exclaim  that  these  several  causes  are  amply  suffi- 
cient to  neutralize  the  power  of  natural  selection.  I  do  not 
believe  so.  But  I  do  believe  that  natural  selection  generally 
acts  very  slowly  in  effecting  changes,  at  long  intervals  of  time, 
and  only  on  a  few  of  the  inhabitants  of  the  same  region.  I 
further  believe  that  these  slow,  intermittent  results  of  natural 
selection  accord  perfectly  with  what  geology  tells  us  of  the 
rate  and  manner  at  which  the  inhabitants  of  the  world  have 
changed. 

Slow  though  the  process  of  selection  may  be,  if  feeble  man 
can  do  much  by  artificial  selection,  I  can  see  no  limit  to  the 
amount  of  change,  to  the  beauty  and  infinite  complexity  of  the 
coadaptations  between  all  organic  beings,  one  with  another  and 
with  their  physical  conditions  of  life,  "which  may  be  effected  in 
the  long  course  of  time  by  Nature's  power  of  selection,  or  the 
survival  of  the  fittest. 

Extinction  caused  by  Natural  Selection, 

This  subject  will  be  more  fully  discussed  in  our  chapter  on 
Geology  ;  but  it  must  be  here  alluded  to  from  being  inti- 
mately connected  with  natural  selection.  Natural  selection 
acts  solely  through  the  preservation  of  variations  in  some  way 
advantageous,  which  consequently  endure.  Owing  to  the  high 
geometrical  ratio  of  increase  of  all  organic  beings,  each  area  is 
already  stocked  with  the  full  number  of  its  existing  inhabit- 
ants, and  as  most  areas  are  already  stocked  with  a  great  diver 
sity  of  forms,  it  follows  that,  as  each  selected  and  favored  form 
increases  in  number,  so  generally  will  the  less  favored  forms 


CriAP.  IV.         EXTINCTION  BY  NATURAL  SELECTION.  109 

decrease  and  l^eooinc  rare.  Rarity,  as  geolo<T:y  tells  us,  is  the 
precursor  to  e.vtinclion.  We  can,  also,  see  that  any  form  rep- 
resented l>y  few  individuals  will,  during  fluctuations  in  the  sea- 
sons or  in  the  numlxir  of  its  enemies,  run  a  good  chance  of 
utter  extinction.  But  we  may  go  further  than  this ;  for,  as 
new  forms  are  continually  and  slowly  being  produced,  unless 
we  believe  that  tlie  mnnber  of  specific  forms  goes  on  perpet- 
ually and  almost  indetinitely  increasing,  many  inevitably  must 
become  extinct.  That  the  number  of  speciiic  forms  has  not 
indcHnitely  increased,  geology  tells  us  plainly ;  and  we  shall 
presently  attempt  to  show  why  it  is  that  the  number  of  species 
throughout  the  world  has  not  become  immeasurably  great. 

AW;  have  seen  tliat  the  species  which  are  most  numerous  in 
individuals  have  the  best  chance  of  producing  favorable  varia- 
tions within  any  given  period.  We  have  evidence  of  this,  in 
the  facts  stated  in  the  second  chapter,  showing  that  it  is  the 
common  species  which  offer  the  greatest  number  of  recorded 
varieties,  or  incipitnit  species.  Hence,  rare  species  will  be  less 
quickly  moditieil  or  improved  within  any  given  period,  and 
they  will  consequently  be  beaten  in  the  race  for  life  by  the 
modified  descendants  of  the  commoner  species. 

From  the  sesevcral  considerations  I  think  it  inevitably  fol- 
lows, that,  as  new  species  in  the  course  of  time  are  formed 
through  natural  selection,  others  will  become  rarer  and  rarer, 
and  finally  extinct.  The  forms  Avhich  stand  in  closest  compe- 
tition with  those  imderg^oing  modification  and  improvement, 
will  naturally  suffer  most.  And  we  have  seen  in  the  chapter 
nn  the  Struggle  for  Existence  that  it  is  the  most  closely-allied 
forms — varieties  of  the  same  species,  and  species  of  the  same 
genus  or  of  related  genera — which,  from  having  nearly  the 
same  structure,  constitution,  and  habits,  generally  come  into 
tlie  severest  competition  with  each  other.  Consequently,  eacli 
new  variety  or  species,  during  the  progress  of  its  formation, 
will  generally  press  hardest  on  its  nearest  kindred,  and  tcTid  to 
exterminate  them.  We  see  tlie  same  process  of  extermination 
among  our  domesticated  productions,  through  the  selection  of 
improved  forms  by  man.  Many  curious  instances  could  l)e  given 
showing  how  quickly  new  breeds  of  cattle,  sheep,  and  other 
animals,  and  varieties  of  flowers,  take  the  place  of  older  and 
inferior  kinds.  In  Yorkshire,  it  is  historically  known  that  the 
ancient  black  cattle  were  displaced  by  the  long-horns,  and  that 
these  "  were  swept  away  by  the  short-horns  "  (I  quote  the 
words  of  an  agricultural  Avriter)  "as  if  by  some  murderous  pes- 
tilence." 


110  DIVERGENCE  OF  CHARACTER.  Chap.  IV. 

Divergence  of  Character, 

The  principle,  which  I  liavc  dcsip^nated  by  this  term,  is  of 
high  importance,  and  cxphiins,  as  I  believe,  several  important 
facts,  in  tlie  first  place,  varieties,  even  strongly-marked  ones, 
though  having  somewhat  of  the  character  of  species — as  is 
shown  by  the  hopeless  doubts  in  many  cases  how  to  rank 
them — yet  certainly  differ  from  each  other  far  less  than  do 
good  and  distinct  species.  Nevertheless,  according  to  my 
view,  varieties  are  species  in  the  process  of  formation,  or  are, 
as  I  have  called  them,  incipient  species.  How,  then,  does  the 
lesser  difference  between  varieties  become  augmented  into  the 
greater  difference  between  species  ?  That  this  does  habitually 
happen,  we  must  infer  from  most  of  the  innumerable  species 
throughout  Nature  presenting  well-marked  differences  ;  where- 
as varieties,  the  supposed  protot}-pes  and  parents  of  future 
well-marked  species,  jiresent  slight  and  ill-defined  differences. 
Mere  chance,  as  we  may  call  it,  might  cause  one  variety  to 
differ  in  some  character  from  its  parents,  and  the  offspring  of 
this  variety  again  to  differ  from  its  parent  in  the  very  same 
character  and  in  a  greater  degree ;  but  this  alone  would  never 
account  for  so  habitual  and  large  a  degree  of  difference  as  that 
between  the  species  of  the  same  genus. 

As  has  always  been  my  practice,  I  have  sought  light  on 
this  head  from  our  domestic  productions.  We  shall  here  find 
something  analogous.  It  will  be  admitted  that  the  produc- 
tion of  races  so  different  as  short-horn  and  Hereford  cattle,  race 
and  cart  horses,  the  several  breeds  of  pigeons,  etc.,  could  never 
have  been  effected  by  the  mere  chance  accumulation  of  varia- 
tions of  a  similar  character  during  many  successive  generations. 
In  ])ractice,  a  fancier  is,  for  instance,  struck  by  a  pigeon  having 
a  sliglitly  shorter  beak ;  another  fancier  is  struck  by  a  pigeon 
having  a  rather  longer  beak ;  and,  on  the  acknowledged  prin- 
ciple that  "  fanciers  do  not  and  will  not  admire  a  medium  stand- 
ard, but  like  extremes,"  they  both  go  on  (as  has  actually  oc- 
curred with  the  sub-breeds  of  the  tumbler-pigeon)  choosing  and 
l)rceding  from  birds  with  longer  and  longer  beaks,  or  with 
shorter  and  shorter  beaks.  Again,  we  may  suppose  that  at  an 
early  period  one  man  preferred  swifter  horses  ;  another  stronger 
and  more  bulky  horses.  The  early  differences  would  be  very 
Blight;  in  the  course  of  time,  from  the  continued  selection  of 
swifter  horses  by  some  breeders,  and  of  stronger  ones  by  others, 
the  differences  would  become  greater,  and  would  be  noted  as 


rnxr.  IV.  DIVERGENCE  or  CHARACTER.  HI 

Ibnnin;^  two  sub-breeds;  finally,  after  the  lapse  of  centuries 
the  sub-breods  would  become  converted  into  two  ■well-estab- 
lished and  distinct  breeds.  As  the  dilVerenccs  slowly  became 
,e:reater,  the  inferior  animals  with  intermediate  characters,  bein;i^ 
neither  very  swift  nor  very  strong,  would  have  been  neglected, 
and  will  have  disappeared.  Here,  then,  we  see  in  man's  pro- 
ductions the  action  of  what  may  be  called  the  principle  of 
divergence,  causing  differences,  at  first  barely  appreciable, 
steadily  to  increase,  and  the  breeds  to  diverge  in  character 
both  from  eacli  other  and  from  their  common  pax-ent. 

But  1»()W,  it  may  be  asked,  can  any  analogous  principle 
apply  in  Nature  ?  t  believe  it  can  and  does  apply  most  effi- 
ciently (though  it  Avas  a  long  time  before  I  saw  how),  from  tlie 
simple  circumstance  that  the  more  diversified  the  descendants 
from  any  one  species  become  in  structure,  constitution,  and 
habrts,  by  so  much  will  they  be  better  enabled  to  seize  on  many 
and  widely-diversified  places  in  the  polity  of  Nature,  and  so  be 
enabled  to  increase  in  numbers. 

We  can  clearly  discern  this  in  the  case  of  animals  with 
simple  habits.  Take  the  case  of  a  carnivorous  quadruped,  of 
which  the  number  that  can  be  supported  in  an}?-  country  has 
long  ago  arrived  at  its  full  average.  If  its  natural  powers  of 
increase  be  allowed  to  act,  it  can  succeed  in  increasing  (the 
country  not  imdergoing  any  change  in  its  conditions)  only  by 
its  varying  descendants  seizing  on  places  at  present  occupied 
by  other  animals:  some  of  them,  for  instance,  being  enabled  to 
feed  on  new  kinds  of  prey,  either  dead  or  alive  ;  some  inhabit- 
ing new  stations,  climbing  trees,  frequenting  water,  and  some 
[lerliaps  becoming  less  carnivorous.  The  more  diversified  in 
lialjits  and  structure  the  descendants  of  our  carnivorous  animal 
lir'came,  the  more  places  they  would  bo  enabled  to  occupy. 
AViiat  applies  to  one  animal  will  apply  throughout  all  time  to 
all  animals — that  is,  if  they  vary — for  otherwise  natural  selec- 
tion can  effect  nothing.  So  it  will  be  witli  j^lants.  It  has  been 
experimentally  proved  that,  if  a  plot  of  ground  be  sown  witli 
one  species  of  grass,  and  a  similar  plot  be  sown  with  several 
distinct  genera  of  grasses,  a  greater  number  of  phmts  and  a 
greater  weight  of  dry  herbage  can  be  raised  by  the  latter  jjro- 
ccss.  Tlie  same  has  been  found  to  hold  good  when  one  va- 
riety and  several  mixed  varieties  of  wlieat  liave  been  sown  on 
equal  spaces  of  ground.  Hence,  if  any  one  species  of  grass 
were  to  go  on  varying,  and  those  varieties  were  continually 
selected  which  differed  from  each  other  in  at  all  the  same  man- 


1  ]  2  DIVERGENCE  OF  CHARACTER.  Chap.  IV, 

lUT  as  distiiKl  species  and  gwiora  of  grasses  differ  from  each 
other,  a  greater  miinber  of  individual  phmts  of  this  species  of 
grass,  inchiding  its  modified  descendants,  ■would  succeed  in 
living  on  the  same  piece  of  ground.  And  we  well  know  that 
each  species  and  each  variety  of  grass  is  aimually  sowing  al- 
most countless  seeds :  and  thus,  as  it  may  be  said,  is  striving 
its  utmost  to  increase  its  numbers.  Consequently,  in  the  course 
of  many  thousand  generations,  the  most  distinct  varieties  of 
any  one  species  of  gTass  would  always  have  the  best  chance  of 
succeeding  and  of  increasing  in  numbers,  and  thus  of  supplant- 
ing the  less  distinct  varieties ;  and  varieties,  when  rendered 
very  distinct  from  each  other,  take  the  rank  of  species. 

The  truth  of  the  principle  that  the  greatest  amount  of  life 
can  be  supported  by  great  diversification  of  structure,  is  seen 
iinder  many  natural  circumstances.  In  an  extremely  small 
area,  especially  if  freely  open  to  immigration,  and  where  the 
contest  between  indivitkial  and  individual  must  be  severe,  we 
always  find  groat  diversity  in  its  inhabitants.  For  instance,  I 
found  that  a  piece  of  turf,  three  feet  by  four  in  size,  which  had 
been  exposed  for  many  years  to  exactly  the  same  conditions, 
supported  twenty  species  of  plants,  and  these  belonged  to 
eighteen  genera  and  to  eight  orders,  which  shoAvs  how  much 
these  plants  differ  from  each  other.  So  it  is  with  tlie  plants 
and  insects  on  small  and  imiform  islets ;  also  in  small  ponds 
of  fresh  water.  Farmers  find  that  they  can  raise  most  food  by 
a  rotation  of  plants  belonging  to  the  most  different  orders : 
Nature  follows  what  may  be  called  a  simultaneous  rotation. 
Most  of  the  animals  and  plants  which  live  close  round  any 
small  piece  of  ground,  could  live  on  it  (supposing  it  not  to  be 
in  any  way  peculiar  in  its  nature),  and  may  be  said  to  be 
striving  to  the  utmost  to  live  there ;  but,  it  is  seen,  that  where 
tliey  come  into  the  closest  competition  with  each  other,  the 
advantages  of  diversification  of  structure,  with  the  accom])any- 
ing  difVerenccs  of  habit  and  constitution,  determine  that  the 
inhabitants,  which  thus  jostle  each  other  most  closely,  shall, 
as  a  general  rule,  belong  to  what  we  call  different  genera  and 
orders. 

The  same  principle  is  seen  in  the  naturalization  of  plants 
through  man's  agency  in  foreign  lands.  It  might  have  been 
expected  that  the  plants  which  would  succeed  in  becoming 
naturalized  in  any  land  would  generally  have  been  closely 
aUied  to  tlie  indigenes  ;  for  these  are  commonly  looked  at  as 
specially  created  and  adapted  for  their  own  country.     It  might 


Chap.  IV.  DIVERGENCE  OF  CnARACTER.  113 

also,  pcrliaps,  liave  been  expected  that  naturalized  plants  would 
have  beloufred  to  a  few  groups  more  especially  adapted  to 
certain  stations  in  their  new  homes.  But  the  case  is  very  dif- 
ferent ;  and  Alpli.  dc  Candolle  has  well  remarked,  in  his  great 
and  admirable  work,  that  floras  gain  by  naturalization,  propor- 
tionally with  the  number  of  the  native  genera  and  species,  far 
more  in  new  genera  than  in  new  species.  To  give  a  single 
instance :  in  tiie  last  edition  of  Dr.  Asa  Gray's  "  Manual  of 
the  Flora  of  the  Northern  United  States,"  260  naturalized 
plants  are  enumerated,  and  these  belong  to  162  genera.  Wc 
thus  see  that  these  naturalized  plants  are  of  a  highly-diversified 
nature.  The}'"  difler,  moreover,  to  a  large  extent,  from  the  in- 
digenes, for,  out  of  the  162  naturalized  genera,  no  less  than  100 
genera  arc  not  there  indigenous,  and  thus  a  large  proportional 
addition  is  made  to  the  genera  now  living  in  the  United  States. 

By  considering  tlie  nature  of  the  plants  or  animals  which 
have  struggled  successfully  with  the  indigenes  of  any  country, 
and  have  there  become  naturalized,  we  may  gain  some  crude 
idea  in  what  manner  some  of  the  natives  would  have  to  be 
modilied,  in  order  to  gain  an  advantage  over  the  other  natives ; 
and  we  may  at  least  safely  infer  that  diversification  of  struc- 
ture, amounting  to  new  generic  differences,  would  be  profit- 
able to  them. 

The  advantage  of  diversification  in  the  inhabitants  of  the 
same  region  is,  in  fact,  the  same  as  that  of  the  physiological 
division  of  labor  in  the  organs  of  the  same  individual  body — 
a  subject  so  well  elucidated  by  Milne  Edwards.  Xo  physiolo- 
gist doubts  that  a  stomach  adapted  to  digest  vegetable  matter 
alone,  or  llesh  alone,  draws  most  nutriment  from  these  sub- 
stances. So  in  the  general  economy  of  an}''  land,  the  more 
widely  and  perfectly  the  animals  and  plants  are  diversified  for 
dilferent  haljits  of  life,  so  will  a  greater  number  of  inchviduals 
be  capable  of  there  sujiporting  themselves.  A  set  of  animals, 
with  their  organization  but  little  diversified,  coulti  hardly  com- 
pete with  a  set  more  perfectly  diversified  in  structure.  It  may 
be  doubt(M],  for  instance,  whether  the  Australian  marsupials, 
which  are  divided  into  groups  differing  but  little  from  each 
other,  and  feebly  representing,  as  Mr,  AVaterhouse  antl  others 
have  remarked,  our  carnivorous,  ruminant,  and  rodent  mam- 
mals, could  successfully  compete  with  these  well-pronounced 
orders.  In  the  Australian  manmials,  we  see  the  process  of 
diversification  in  an  early  and  incomplete  stage  of  develop- 
ment. 


I  ]  t  RESULTS   OF  THE  ACTION  OF  Chap.  IV, 

Tlie  Pi'ohdhle  Results  of  the  Action  of  Katural  Selection 
through  Diverrjence  of  Character  and  JSxtinctiony  vi  the 
Descendants  of  a  Common  Ancestor. 

After  tlie  forcg'oing  discussion,  which  has  been  much  com- 
pressed, we  may  assume  that  the  modified  descendants  of  any 
one  species  Avill  succeed  by  so  much  the  better  as  they  become 
more  diversified  in  structure,  and  are  thus  enabled  to  encroach 
on  places  occupied  by  other  beings.  Now  let  us  see  how  this 
principle  of  benefit  being  derived  from  divergence  of  character, 
combined  with  the  principles  of  i>atural  selection  and  of  ex- 
tinction, tends  to  act. 

The  accompanying  diagram  will  aid  us  in  understanding 
this  rather  perplexing  subject.  Let  A  to  L  represent  the  spe- 
cies of  a  genus  large  in  its  own  country ;  these  species  are 
supposed  to  resemble  each  other  in  unequal  degrees,  as  is  so 
generally  the  case  in  Nature,  and  as  is  represented  in  the 
cliagram  by  the  letters  standing  at  unequal  distances.  I  have 
said  a  large  genus,  because  Ave  have  seen  in  the  second  chap- 
ter that,  on  an  average,  more  of  the  species  of  large  genera 
vary  than  of  small  genera ;  and  the  varying  species  of  the 
large  genera  present  a  greater  number  of  varieties.  We  have, 
also,  seen  that  the  species,  which  are  the  commonest  and  the 
most  widely-diilused,  vary  more  than  do  the  rare  and  restricted 
species.  Let  (A)  be  a  common,  widely-diffused,  and  varying 
species,  belonging  to  a  genus  large  in  its  own  country.  The 
branching  and  diverging  dotted  lines  of  unequal  lengths  pro- 
ceeding from  (A),  may  represent  its  varying  offspring.  The 
variations  are  supposed  to  be  extremely  slight,  but  of  the  most 
diversified  nature ;  they  are  not  supposed  all  to  appear  simul- 
taneously, but  often  after  long  intervals  of  time ;  nor  are  they 
all  supposed  to  endure  for  equal  periods.  Only  those  varia- 
tions which  are  in  some  Avay  profitable  will  be  preserved  or 
naturally  selected.  And  here  the  importance  of  the  principle 
of  benefit  being  derived  from  divergence  of  character  comes 
in ;  for  this  will  generally  lead  to  the  most  different  or  diver- 
gent variations  (represented  by  the  outer  dotted  lines)  being 
preserved  and  accumulated  by  natural  selection.  When  a  dot- 
ted line  reaches  one  of  the  horizontal  lines,  and  is  there  marked 
by  a  small  numbered  letter,  a  sufficient  ainount  of  variation  is 
supjiosed  to  have  been  accunuilated  to  have  formed  a  fairly 
well-marked  variety,  such  as  would  l)e  thought  worthy  of  rec- 
ord in  a  systematic  work. 


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Chap.  IV.  NATURAL  SELECTION.  1  ]  5 

The  intervals  between  the  horizontal  lines  in  the  dia^ara, 
may  ix'prescnt  each  a  thousand  generations,  or  ten  thousand. 
After  a  thousand  generations,  species  (A)  is  supposed  to  have 
produced  two  fairly  well-marked  varieties,  namely  a}  and  rn). 
These  two  varieties  will  generally  continue  to  be  exposed  to 
the  same  conditions  Avhich  made  their  parents  variable,  and 
the  tendency  to  variability  is  in  itself  hereditary,  consequently 
tliey  will  tend  to  vary,  and  generally  to  vary  in  nearl}'  the 
same  manner  as  their  j)arents  varied.  Moreover,  these  two 
varieties,  being  only  slightl^'-niodilied  forms,  will  tend  to  in- 
herit those  advantages  which  made  their  parent  (A)  more 
numerous  than  most  of  the  other  inhabitants  of  the  same  coun- 
try ;  they  will  likewise  partake  of  those  more  general  advan- 
tages v/hich  made  the  genus  to  which  the  parent-species  be- 
longed a  large  genus  in  its  ov,n  country.  And  these  circinn- 
stanccs  we  know  to  bo  favoral)le  to  tiic  production  of  new 
varieties. 

If,  then,  these  two  varieties  be  variable,  the  most  divergent 
of  their  variations  will  generally  be  ])reserved  during  the  next 
thousand  generations.  And  after  this  interval,  variety  0}  is 
supposed  in  the  diagram  to  have  pi'oduccd  variety  a^,  which 
will,  owing  to  the  principle  of  divergence,  difler  more  from  (A) 
than  did  variety  a*.  Variety  «^'  is  supposed  to  have  produced 
two  varieties,  namely  Wi"  and  s",  diflering  from  each  other,  and 
more  considerably  from  their  common  parent  (A).  Wc  may 
continue  the  process  by  similar  steps  for  any  length  of  time ; 
some  of  the  varieties,  after  each  thousand  generations,  produ- 
cing only  a  single  variety,  but  in  a  more  and  more  modi  lied  con- 
dition, some  producing  two  or  three  varieties,  and  some  failing 
to  produce  any.  Thus  the  varieties,  or  modified  descendants, 
proceeding  from  the  common  ])arent  (A),  will  generally  go  on 
increasing  in  numljcr,  and  diverging  in  character.  In  the  dia- 
gram tlie  process  is  represented  up  to  the  ten-thousandth  gen- 
eration, and  under  a  condensed  and  siniplilled  form  up  to  the 
fourteen-thousandth  generation, 

IJut  I  must  hen;  remark  that  I  do  not  suppose  that  the 
process  ever  goes  on  so  regularly  as  is  represented  in  the  dia- 
gram, though  in  itself  made  somewhat  irregular,  nor  that  it 
goes  on  continuously ;  it  is  far  more  ])robable  that  each  form 
remains  for  long  periods  unaltered,  and  tlien  again  imdcr- 
gocs  modification.  Nor  do  I  suppose  that  the  most  di- 
vergent varieties  are  invariably  preserved:  a  medium  form 
may  often  long  endure,  and  may  or  may  not  produce  more 


IIG  RESULTS   OF  THE  ACTION  OF  C'kap.  TV. 

than  one  modified  descendant;  for  nalural  selection  Avill  al- 
ways act  according  to  the  nature  of  the  places  which  arc  either 
unoccupied  or  not  perfectly  occupied  by  other  beings ;  and 
this  will  depend  on  infinitely-complex  relations.  But,  as  a 
general  ruh>,  the  more  diversified  in  structure  tlic  descendants 
from  any  one  species  can  be  rendered,  the  more  places  they 
will  be  enabled  to  seize  on,  and  the  more  their  modified  pro- 
geny will  increase.  In  our  diagram  the  line  of  succession  is 
liroken  at  regular  intervals  by  small  numbered  letters  marking 
the  succ(>ssivc  forms  which  have  become  sufficiently  distinct  to 
be  recorded  as  varieties.  But  these  breaks  are  imaginary,  and 
might  have  been  inserted  an^^vhere,  after  intervals  long 
enough  to  have  allowed  the  accumulation  of  a  considerable 
amount  of  divergent  variation. 

As  all  the  modified  descendants  from  a  common  and  wide- 
ly-diffused species,  belonging  to  a  large  genus,  Avill  tend  to 
partake  of  the  same  advantages  which  made  their  parent  suc- 
cessful in  life,  they  will  generally  go  on  multiplying  in  number 
as  well  as  diverging  in  character:  this  is  represented  in  the 
diagram  by  the  several  divergent  branches  proceeding  from 
(A).  The  modified  offspring  from  the  latter  and  more  highly- 
improved  branches  in  the  lines  of  descent,  will,  it  is  probable, 
often  take  the  place  of,  and  so  destroy,  the  earlier  and  less  im- 
j)i(ived  branches :  this  is  represented  in  the  diagram  by  some 
of  the  lower  branches  not  reaching  to  the  upper  horizontal 
lines.  In  some  cases  I  do  not  doubt  that  the  jirocess  of  modi- 
fication will  be  confined  to  a  single  line  of  descent,  and  the 
ntunber  of  the  descendants  Mill  not  be  increased;  althouglithe 
amount  of  divergent  modification  may  have  been  increased  in 
the  successive  generations.  This  case  would  be  represented  in 
tlic  diagram,  if  all  the  lines  proceeding  from  (A)  Avere  removed, 
excepting  that  from  «*  to  rt'°.  In  the  same  way,  for  instance,  the 
English  race-horse  and  English  pointer  have  apparently  both 
gone  on  slowly  diverging  in  character  from  their  original  stocks, 
Mithout  either  having  given  oft'  any  fresh  branches  or  races. 

After  ten  thousand  generations,  species  (A)  is  sujiposed  to 
liave  produced  three  forms,  «",/'",  and  wi",  which,  from  hav- 
ing diverged  in  character  during  the  successive  generations, 
will  have  come  to  differ  largely,  but  jicrhaps  unequally,  from 
each  other  and  from  their  common  jvarcnt.  If  we  suppose  the 
amount  of  change  between  each  horizontid  line  in  our  diagram 
to  be  excessively  small,  these  three  forms  may  still  be  only 
w('ll-mark,Ml  varieties  ;  but  we  have  only  to  suppose  the  steps 


Chap.  IV.  NATURAL  SELECTION.  117 

ill  tiie  process  of  modification  to  be  more  numerous  or  j^rcatcr 
in  amount,  to  convert  these  three  forms  into  doubtful  or  at 
last  wcU-denncd  species :  thus  the  diao^ram  iUustratcs  the 
steps  by  wliich  the  small  diflerences  distinguishing  varieties 
are  increased  into  the  larger  differences  distinguishing  species. 
By  continuing  the  same  process  for  a  greater  number  of  gener- 
ations (as  shown  in  the  diagram  in  a  condensed  and  simplified 
manner),  we  get  eight  species,  marked  by  the  letters  between 
«"  and  m^\  all  descended  from  (A).  Thus,  as  I  believe,  spe- 
cies are  multiplied  and  genera  are  formed. 

In  a  large  genus  it  is  probable  that  more  than  one  species 
would  vary.  In  the  diagram  I  have  assumed  that  a  second 
species  (I)  has  produced,  by  analogous  steps,  after  ten  thou- 
sand generations,  either  two  well-marked  varieties  (w'°  and  z'") 
or  two  species,  according  to  the  amount  of  change  supposed  to 
be'rcjircsented  between  the  horizontal  lines.  After  fourteen 
thousand  generations,  six  new  species,  marked  by  the  letters 
w'*  to  z'*,  are  supposed  to  have  been  produced.  In  any  genus, 
the  species  which  are  already  very  different  in  character  from 
each  other  will  generally  tend  to  produce  the  greatest  num- 
ber of  modified  descendants ;  for  they  will  have  the  best 
chance  of  filling  new  and  widely-different  places  in  the  polity 
of  Nature :  hence  in  the  diagram  I  have  chosen  the  extreme 
species  (A),  and  the  nearly  extreme  species  (I),  as  those  which 
have  largely  varied,  and  have  given  rise  to  new  varieties  and 
species.  The  other  nine  species  (marked  by  capital  letters) 
of  our  original  genus,  may  for  long  but  unequal  periods  con- 
tinue to  transmit  unaltered  descendants  ;  -and  this  is  shown  in 
tlu;  diagram  by  the  dotted  lines  unequally  prolonged  upward. 

But  during  the  process  of  modification,  represented  in  the 
diagram,  another  of  our  principles,  namely,  that  of  extinction, 
will  have  played  an  important  part.  As  in  each  fully-stocked 
country  natural  selecti(jn  necessarily  acts  by  the  selected  form 
having  some  advantage  in  the  struggle  for  life  over  other  forms, 
there  will  be  a  constant  tondcMicy  in  the  improved  descendants 
of  any  one  species  to  supplant  and  exterminate  in  each  stage 
of  descent  their  pred(X"essors  and  their  original  progenitor. 
For  it  should  be  remembered  that  the  competition  will  gen- 
erally be  most  severe  between  those  forms  which  are  most 
nearly  related  to  each  other  in  habits,  constitution,  and  struc- 
ture. Hence  all  the  intermediate  forms  between  the  earlier 
and  later  states,  that  is,  between  the  less  and  more  improved 
states  of  a  species,  as  well  as  the  original  parent-species  itself. 


lis  RESULTS   OF  THE   ACTION   OF  Chap.  IV. 

will  generally  tend  to  l^ecome  extinct.  So  it  probably  Avill 
be  ^vith  many  -whole  collateral  lines  of  descent,  Avhich  ^vill  be 
conquered  by  later  and  improved  lines  of  descent.  If,  liow- 
ever,  the  modified  offspring  of  a  species  get  into  some  distinct 
country,  or  become  quickly  adapted  to  some  cjuite  new  station, 
in  whic-h  offspring  and  progenitor  do  not  come  into  compe- 
tition, both  may  continue  to  exist. 

If,  then,  our  diagram  be  assumed  to  represent  a  consider- 
able amount  of  modification,  species  (A)  and  all  the  earlier  va- 
rieties Avill  have  become  extinct,  having"  been  replaced  by  eight 
new  species  (a"  to  wi")  ;  and  (I)  will  have  been  replaced 
by  six  (?i"  to  2'*)  new  species. 

But  we  may  go  further  than  this.  The  original  species 
of  our  genus  were  supposed  to  resemble  eacli  other  in  unequal 
degrees,  as  is  so  generally  the  case  in  Nature ;  species  (A) 
being  more  nearly  related  to  B,  C,  and  D,  than  to  the  other 
species ;  and  species  (I)  more  to  G,  H,  K,  L,  than  to  the 
others.  These  two  species  (A)  and  (I)  were  also  supposed  to 
be  very  common  and  widely-dilfuscd  species,  so  that  they  must 
originally  have  had  some  advantage  over  most  of  the  other 
species  of  the  genus.  Their  modified  descendants,  fourteen  in 
number  at  the  fourteen-thousandth  generation,  will  probably 
have  inherited  some  of  the  same  advantages  :  they  have  also 
been  modified  and  improved  in  a  diversified  manner  at  each 
stage  of  descent,  so  as  to  have  become  adapted  to  many  related 
places  .in  the  natural  economy  of  their  country.  It  seems, 
therefore,  extremely  probable  that  they  will  have  taken  the 
places  of,  and  thus  exterminatod,  not  only  their  parents  (A) 
and  (I),  but  likewise  some  of  the  original  species  which  were 
most  nearly  related  to  their  parents.  Hence  very  few  of  the 
original  species  will  have  transmitted  offspring  to  the  fourteen- 
tliousandth  generation.  AVe  may  suppose  that  only  one  (F), 
of  the  two  species  (E  and  F)  which  were  least  closely  related 
to  the  other  nine  original  species,  has  transmitted  descendants 
to  this  late  stage  of  descent. 

The  new  species  in  our  diagram,  descended  from  the  origi- 
nal eleven  species,  will  now  be  lifteen  in  number.  Owing  to 
the  divergent  tendency  of  natural  selection,  the  extreme 
amoimt  of  difference  in  character  betAveen  species  «'*  and  2'* 
will  be  much  greater  than  that  between  the  most  distinct  of 
the  original  eleven  species.  The  new  species,  moreover,  wiK 
be  allied  to  each  other  in  a  Avidely-differcnt  manner.  Of  the 
eight  descendants  from  (A)  the  three  marked  a",  <j^\  p^\  will 


CiiAr.  IV.  NATUEAL  SELECTION.  119 

bo  noavly  related  from  liaving^  recently  branched  off  from  a'°/ 
J/*,  and  /'*,  from  liavin":  diverged  at  an  earlier  period  from  a'', 
\\\\\  be  in  some  deo^ree  distinct  from  the  three  first-named  spe- 
ties ;  and  lastly,  o'\  e'*,  and  »i'*,  will  be  nearly  related  one  to 
the  other,  but,  from  havinfj;  diverf^ed  at  the  first  commence- 
ment of  tlie  process  of  modification,  will  be  widely  different 
from  the  other  five  species,  and  may  constitute  a  sub-genus  or 
a  distinct  genus. 

The  six  descendants  from  (I)  will  form  two  sub-genera  or 
genera.  But  as  the  original  species  (I)  differed  largely  from 
(A),  standing  nearly  at  the  extreme  end  of  the  original  genus, 
llie  six  descendants  from  (I)  will,  owing  to  inheritance  alone, 
differ  considerably  from  the  eight  descendants  from  (A)  ;  the 
two  groups,  moreover,  are  supposed  to  have  gone  on  diverging 
in  different  directions.  The  intermediate  species,  also  (and 
this  is  a  very  important  consideration),  which  connected  the 
original  species  (A)  and  (I),  have  all  become,  excepting  (F), 
extinct,  and  have  left  no  descendants.  Hence  the  six  new  spe- 
cies descended  from  (I),  and  the  eight  descended  from  (A), 
will  have  to  be  ranked  as  very  distinct  genera,  or  even  as  dis- 
tinct sub- families. 

Thus  it  is,  as  I  believe,  that  two  or  more  genera  are  pro- 
duced, by  descent  Avith  modification,  from  two  or  more  species 
of  the  same  genus.  And  the  two  or  more  parent-species  are 
supposed  to  have  descended  from  some  one  species  of  an  ear- 
lier genus.  In  our  diagram,  this  is  indicated  by  the  broken 
lines,  beneath  the  capital  letters,  converging  in  sub-branches 
downward  toward  a  single  point;  this  point  representing  a 
single  species,  the  supposed  progenitor  of  our  several  new  sub- 
genera and  genera. 

It  is  worth  while  to  reflect  for  a  moment  on  the  character 
of  the  new  species  f'*,  which  is  supposed  not  to  have  diverged 
much  in  character,  but  to  have  retained  the  fomi  of  (F),  either 
unaltered  or  altered  only  in  a  slight  degree.  In  this  case,  its 
allinitics  to  the  other  fourteen  new  species  Avill  be  of  a  curious 
and  circuitous  nature.  Having  descended  from  a  form  which 
stood  l)etwe(Mi  the  two  parent-species  (A)  and  (I),  now  sup- 
posed to  1)0  extinct  and  imknown,  it  will  be  in  some  degree  in- 
l«-rmediate  in  character  between  the  two  groups  descended 
from  these  species.  I5ut  as  these  two  groups  have  gone  on 
diverging  in  character  from  the  type  of  their  parents,  the  new 
species  (f'*)  will  not  be  directly  intermediate  between  them, 
but    ratlier   l^etween    t}^es  of  the   two   groups;    and   every 


120  RESULTS  OF  NATURAL  SELECTION.  Chap.  IV. 

naturalist  will  be  able  to  bring  some  such  case  before  his 
mind. 

In  the  diagram,  each  liorizonal  line  has  hitherto  been  sup- 
posed to  represent  a  tliousand  generations,  but  each  may  rep- 
resent a  million  or  several  million  generations ;  it  may  also 
represent  a  section  of  the  successive  strata  of  the  earth's  crust 
including  extinct  remains.  '  We  shall,  when  we  come  to  our 
chapter  on  Geology,  have  to  refer  again  to  this  subject,  and  I 
think  we  shall  then  sec  that  the  diagram  throws  light  on  the 
affinities  of  extinct  beings,  Avhich,  though  generally  belonging 
to  the  same  orders,  or  families,  or  genera,  ■with  those  now  liv- 
ing, yet  are  often,  in  some  degree,  intermediate  in  character 
between  existing  groups  ;  and  we  can  understand  this  fact,  for 
the  extinct  species  lived  at  very  ancient  epochs  when  the 
branching  lines  of  descent  had  diverged  less. 

I  see  no  reason  to  limit  the  process  of  modification,  as  now 
explained,  to  the  formation  of  genera  alone.  If,  in  the  diagram, 
we  suppose  the  amount  of  change  represented  by  each  succes- 
sive group  of  diverging  dotted  lines  to  be  great,  the  forms 
marked  a'*  to^J>",  those  marked  i'*  and/"'\  and  those  marked 
o'*  to  ni^*,  will  form  three  very  distinct  genera.  We  shall  also 
have  two  very  distinct  genera  descended  from  (1),  differing 
widely  from  the  descendcnts  of  (A).  These  two  groups  of 
genera  will  thus  form  two  distinct  families,  or  orders,  accord- 
ing to  the  amount  of  divergent  modification  supposed  to  be 
represented  in  the  diagram.  And  the  two  new  families,  or 
orders,  are  descended  from  two  species  of  the  original  genus, 
and  these  are  suj^posed  to  be  descended  from  some  still  more 
ancient  and  unknown  form. 

We  have  seen  that  in  each  countrj^  it  is  the  species  belong- 
ing to  the  larger  genera  which  oftcnest  present  varieties  or  in- 
cipient species.  This,  indeed,  might  have  been  expected ;  for 
as  natural  selection  acts  throvigh  one  form  having  some  advan- 
tage over  other  forms  in  the  struggle  for  existence,  it  will 
chiefly  act  on  those  which  already  have  some  advantage ;  and 
the  largeness  of  any  grouji  shows  that  its  species  have  inherited 
from  a  connnon  ancestor  some  advantage  in  common.  Hence, 
the  struggle  for  the  production  of  new  and  modified  descend- 
ants will  mainly  lie  between  the  larger  groups  which  are  all 
trying  to  increase  in  number.  One  large  grouj)  will  slowl}' 
ct)nfjuer  another  large  group,  reduce  its  numbers,  and  thus  les- 
sen its  chance  of  further  variation  and  improveuKMit.  Within 
the  same  large  group,  the  later  and  more  highly -perfected  su]> 


Caw.  IV.  ADVANCE  OF  ORGANIZATION.  121 

j^roups,  from  hraneliiiig"  out  and  seizinc^  on  many  new  plar-cs  in 
the  polity  of  Nature,  will  constantly  tend  to  sujiplant  and  de- 
stroy the  earlier  and  Icss-iinp.roved  svib-<^oups.  Small  and 
broken  ""roups  and  sul>irroups  will  hnally  disappear,  Lookinnf 
to  the  future,  Ave  can  ])redict  that  the  groups  of  organic  beings 
which  are  now  large  and  triumphant,  and  Avbich.are  least 
broken  u]i,  that  is,  which  as  yet  have  sulTered  least  extinction, 
will  for  a  long  period  continue  to  increase.  But  which  groups 
will  ultimately  prevail,  no  man  can  predict ;  for  we  well  know 
that  many  groups  formerly  most  extensively  develojied,  have 
now  become  extinct.  Looking  still  more  remotely  to  the 
future,  we  may  predict  that,  owing  to  the  continued  and  steady 
increase  of  the  larger  groups,  a  multitude  of  smaller  groups  will 
become  utterly  extinct,  and  leave  no  modified  descendants; 
and  consequently  that,  of  the  species  living  at  any  one  period, 
extremely  (gw  will  transmit  descendants  to  a  remote  futurity. 
I  shall  have  to  return  to  this  subject  in  the  chapter  on  Classifi- 
cation, but  I  may  add  that  as  according  to  this  view  extremely 
few  of  the  more  ancient  species  have  transmitted  descendants, 
and  as  :ill  the  descendants  of  the  same  species  form  a  class,  we 
can  imdcrstand  how  it  is  that  there  exist  so  few  classes  in  each 
main  division  of  the  animal  and  vegetable  kingdoms.  Although 
few  of  the  most  ancient  species  have  left  motlified  descendants, 
yet,  at  remote  geological  periods,  the  earth  may  have  been 
almost  as  well  jjcopled  with  species  of  many  genera,  families, 
oiders,  and  classes,  as  at  the;  present  day. 

O71  the  Degree  to  which  Organization  tends  to  advance. 

Natural  Selection  exclusively  acts  by  the  preservation  and 
accunmlation  of  variations,  which  are  beneficial  under  the  or- 
ganic and  inorganic  conditions  of  life  to  which  each  creature  is 
exposed  at  each  successive  period  of  life.  The  ultimate  result 
is,  that  each  creature  tends  to  become  more  and  more  improved 
in  relation  to  its  conditions.  This  improvement  inevitably 
leads  to  the  gradual  advancement  of  the  organization  of  the 
greater  number  of  living  bi'ings  throughout  the  world.  But 
here  we  enter  on  a  very  intricate  subject,  for  naturalists  have 
not  defined  to  each  other's  satisfaction  what  is  meant  by  an 
advance  in  org-anization.  Among  the  vertcbrata  the  degree  of 
intellect  and  approac-h  in  structure  to  man  clearly  come  into 
play.  It  might  be  thought  that  the  amount  of  change  Avhich 
the  various  ])arts  and  organs  pass  through  in  their  develop- 
G 


['^2  <JN  THE  DEGKEE  TO    WHICH  Cuap.  IV. 

incnt  from  the  cnil)ryo  to  maturity  would  suffice  as  a  standard 
of  comparison ;  but  there  are  cases,  as  with  certain  parasitic 
crustaceans,  in  Avhich  several  parts  of  the  structure  become 
less  perfect,  so  that  the  mature  animal  cannot  be  called  higher 
than  its  larva.  Von  Baers  standard  seems  the  most  widely 
applica])le  and  the  Ix'st,  namely,  the  amount  of  diflerentiation 
of  the  diiferent  parts  of  the  same  organic  being,  in  the  adult 
state  as  I  should  be  inclined  to  add,  and  their  specialization 
for  difl'ercnt  functions  ;  or, -as  Milne  Edwards  would  express  it, 
the  completeness  of  the  division  of  physiological  labor.  But  we 
shall  sec  how  obscure  this  subject  is  if  Ave  look,  for  instance,  to 
fish,  among  which  some  naturalists  rank  those  as  highest  which, 
like  the  sliarks,  approach  nearest  to  amphibians ;  while  other 
naturalists  rank  the  common  bony  or  teleostean  fishes  as  the 
highest,  inasmuch  as  they  are  most  strictly  fish-like,  and  differ 
most  from  the  other  vertebrate  classes.  Still  more  plainly  we 
see  the  obscurity  of  the  subject  by  turning  to  plants,  among 
which  the  standard  of  intellect  is  of  course  quite  excluded  ;  and 
here  some  botanists  rank  those  plants  as  highest  which  have 
every  organ,  as  sepals,  jietals,  stamens,  and  pistils,  fully  devel- 
oped in  each  flower ;  whereas  other  botanists,  probably  with 
more  truth,  look  at  the  plants  which  have  their  several  organs 
much  modified  and  reduced  in  number  as  the  highest. 

If  we  take,  as  the  standard  of  high  organization,  the 
amount  of  differentiation  and  speciahzation  of  the  several  or- 
gans in  each  being  when  adult  (and  this  will  include  the  ad- 
vancement of  the  brain  for  intellectual  purposes),  natural  selec- 
tion clearly  leads  toward  highness  ;  for  all  physiologists  admit 
that  the  specialization  of  organs,  inasmuch  as  they  perform  in 
this  state  their  functions  better,  is  an  advantage  to  each  being; 
and  hence  the  accumulation  of  variations  tending  toward  spe- 
cialization is  within  the  scope  of  natural  selection.  On  the 
other  hand,  Ave  can  see,  bearing  iu  mind  that  all  organic  beings 
are  striving  to  increase  at  a  high  ratio  and  to  seize  on  every 
ill-occupied  place  in  the  economy  of  Nature,  that  it  is  quite  pos- 
sible for  natural  selection  gradually  to  fit  an  organic  being  to 
a  situation  in  AA'hich  scA^eral  organs  would  be  superfluous  or 
useless  :  in  such  cases  there  might  be  retrogression  in  the  scale 
of  organization,  AN'hcther  organization  on  the  Avhole  has 
actually  adA'anced  from  the  remotest  geological  jieriods  to  the 
present  day  Avill  be  more  conveniently  discussed  in  om-  chapter 
on  Geological  Succession. 

But  it  may  be  objected  that,  if  all  organic  beings  thus  tend 


1 


C;i.\r.  IV.  ORGANIZATION  TENDS  TO  ADVANCE.  123 

to  rise  iu  llie  scale,  liow  is  it  that  throughout  tlie  Avorkl  a  mul- 
titude of  the  lowest  forms  still  exist ;  and  how  is  it  that  in 
each  great  class  some  forms  are  far  more  hiofhly  developed  than 
otliers  ?  Why  have  not  the  more  highly-developed  forms 
everywhere  supplanted  and  exterminated  the  lower?  Lamarck, 
who  lielieved  iu  an  innate  and  ineWtable  tendency  toward  per- 
fection in  all  organic  beings,  seems  to  have  felt  this  difficulty 
so  strongly,  that  he  was  led  to  suppose  that  new  and  simple 
forms  are  continually  being  produced  by  spontaneous  genera- 
tion. Science,  however,  under  her  present  aspect  does  not 
countenance  tlie  belief,  whatever  the  futiu-e  may  reveal,  that 
living  creatures  are  now  being  generated.  On  our  theory  the 
continued  existence  of  lowly  organisms  oflcrs  no  difficulty  ;  for 
natural  selection,  or  the  survival  of  the  fittest,  does  not  neces- 
sarily include  progressive  development — it  only  takes  advan- 
tage of  "such  variations  as  arise  and  are  bcnetlcial  to  each  crea- 
ture imder  its  complex  relations  of  life.  And  it  may  be  asked 
what  advantage,  as  far  as  we  can  see,  would  it  be  to  an  infu- 
sorian  animalcule — to  an  intestinal  worm — or  even  to  an  earth- 
worm, to  be  highly  organized?  If  it  were  no  advantage,  tlu^se 
forms  would  be  left  by  natural  selection  miimproved  or  but 
little  improved;  and  might  remain  for  indefmite  ages  in  their 
present  little  advanced  condition.  And  geology  tells  us  that 
some  of  the  lowest  forms,  as  the  infusoria  and  rizopods,  have 
remained  for  an  enormous  period  in  nearly  their  present  state. 
But  to  suppose  that  most  of  the  many  now  existing  low  forms 
have  not  in  the  least  advanced  since  the  first  dawn  of  life 
would  be  rash ;  for  every  naturalist  who  has  dissected  some  of 
the  beings  now  ranked  as  very  low  in  the  scale,  must  have 
been  struck  with  their  really  wondrous  and  beautiful  organ- 
zation. 

Nearly  the  same  remarks  are  applicable  if  we  look  to  the 
dilVt -rent  grades  of  organization  within  each  great  group;  for 
instance,  in  the  vertebrata,  to  the  coexistence  of  manunals  and 
fish — among  manunalia,  to  the  coexistence  of  man  and  tlu; 
ornitliorliynchus — among  fishes,  to  the  coexistence  of  the  shark 
and  lancelet  (Brancliiostoma),  which  latter  fish  in  the  extreme 
8imi)licily  of  its  structiue  approaches  the  invertebrate  classes. 
But  mammals  and  fisli  hardly  come  into  competition  with  each 
other ;  tiie  advancement  of  tlie  whole  class  of  mammals,  or  of 
certain  memb(^rs  in  this  class,  to  the  highest  grade  would  not 
lead  to  their  taking  the  place  of,  and  thus  exterminating,  fishes. 
Physiologists  believe  that  the  brain  must  be  bathed  by  warm 


12i  ADVANCE  OF  ORGANIZATION.  Chap.  IV. 

blood  to  be  highly  active,  and  tliis  I'cquires  auiial  respiration  ; 
so  that  Avarm-bloodod  maininals  when  inhabiting  the  water  live 
under  some  disadvantages  in  comparison  with  iishes.  In  this 
latter  class,  members  of  the  shark  family  would  not  tend  to 
supplant  the  lancelet ;  for  the  lancelet,  as  I  hear  from  Fritz 
Miiller,  has,  as  sole  companion  and  competitor  on  the  barren, 
sandy  shore  of  South  Brazil,  an  anomalous  annelid.  The  three 
lowest  orders  of  mammals,  namely,  marsupials,  edentata,  and 
rodents,  coexist  in  South  America  in  the  same  region  with 
numerous  monkeys,  and  probably  interfere  little  with  each 
other.  Altliougli  oi'ganization,  on  the  whole,  may  have  ad- 
vanced and  be  still  advancing  throughout  the  world,  yet  the 
scale  will  always  present  many  degrees  of  perfection;  for  the 
high  advancement  of  certain  whole  classes,  or  of  certain  mem- 
bers of  each  class,  does  not  at  all  necessarily  lead  to  the  ex- 
tinction of  those  groups  with  Avhich  they  do  not  enter  into 
close  competition.  In  some  cases,  as  we  shall  hereafter  see, 
lowly-organized  forms  appear  to  have  been  preserved  to  the 
present  day  from  inhabiting  confmed  or  peculiar  stations,  where 
they  have  been  subjected  to  less  severe  competition,  and  where 
their  scant}-  numbers  have  retarded  the  chance  of  favorable 
variations  arising. 

Finally,  I  believe  that  many  lowly-organized  forms  now 
exist  throughout  the  Avorld,  from  various  causes.  In  some 
cases  variations  or  individual  differences  of  a  favorable  nature 
may  never  have  arisen  for  natural  selection  to  act  on  and 
accumulate.  In  no  case,  probably,  has  time  sufficed  for  the 
utmost  possible  amount  of  development.  In  some  few  cases 
there  has  been  Avhat  we  must  call  retrogression  of  organization. 
But  the  main  cause  lies  in  the  fact  that  under  very  simple  con- 
ditions of  life  a  high  organization  would  be  of  no  service — 
possibly  would  be  of  actual  disservice,  as  being  of  a  more 
delicate  nature,  and  more  liable  to  be  put  out  of  order  and 
injured. 

Looking  to  the  first  dawn  of  life,  when  all  organic  beings, 
as  w^e  may  believe,  presented  the  simplest  structun^,  how,  it 
has  been  asked,  couhl  the  first  steps  in  the  advancement  or 
differentiation  of  parts  have  arisen'?  Mr.  Herbert  S])encer 
would  probably  answer  that  as  soon  as  simple  unicellular  or- 
ganism came  by  growth  or  division  to  be  coinj^ounded  of  sev- 
eral cells,  or  became  attached  to  any  supporting  surface,  his 
law  "  that  homologous  imits  of  any  order  become  ilifferentiated 
in  proportion  as  their  relations  to  incident  forces  become  differ- 


CiiAP.  IV.  VARIOUS  OBJECTIONS.  125 

eiit,"  would  come  into  action.  But  as  we  have  no  facts  to 
guide  us,  all  speculation  on  the  subject  is  useless.  It  is,  how- 
ever, an  en-or  to  suppose  that  there  would  be  no  struggle  for 
existence,  and,  conseciuently,  no  natural  selection,  until  many 
forms  had  been  produced :  variations  in  a  single  species  in- 
habiting an  isolated  station  might  be  beneficial,  and  thus  the 
Avhole  mass  of  individuals  might  be  modified,  or  two  distinct 
forms  might  arise.  But,  as  I  remarked  toward  the  close  of  the 
Introduction,  no  one  ought  to  feel  surprise  at  much  remaining 
as  yet  unexplained  on  the  origin  of  species,  if  we  make  due 
allowance  for  our  profound  ignorance  on  the  mutual  relations 
of  the  inhabitants  of  the  world  during  the  past  epochs  in  its 
historj'. 

Various  Objectiofis  considered. 

I  will  here  notice  a  few  miscellaneous  objections  Avhich 
nave  been  advanced  against  my  views,  as  some  of  the  previous 
discussions  may  perhaps  thus  be  made  clearer;  but  it  would 
be  useless  to  discuss  all  of  them,  as  many  have  been  made  by 
writers  Avho  have  not  taken  the  trouble  to  understand  my  views. 
Thus  a  distinguished  German  naturalist  has  recently  asserted 
that  the  weakest  part  of  my  theory  is,  that  I  consider  all  or- 
ganic beings  as  imperfect :  what  I  have  really  said  is,  that  all 
are  not  as  ]ierfect  in  relation  to  their  conditions  as  they  might 
be ;  and  this  is  shown  to  be  the  case  by  so  many  native  forms 
in  many  quarters  of  the  world  yielding  their  places  to  intrud- 
ing foreigners  which  have  become  naturalized.  Nor  can  all 
organic  beings,  even  if  they  were  at  any  one  time  perfectly 
adapted  to  their  conditions  of  life,  remain  so,  when  the  condi- 
tions slowly  change,  unless  they  likewise  change;  and  no  one 
will  dispute  that  the  physical  conditions  of  each  country,  as 
well  as  the  numbers  and  kinds  of  its  inhabitants,  are  liable  to 
change. 

It  has  been  argued  that,  as  none  of  the  animals  and  plants 
of  Egypt,  of  which  we  know  any  thing,  have  clianged  dining 
the  last  3,000  years,  so  pro1)ably  none  have  been  modified  in 
any  other  part  of  the  world.  The  many  animals  which  have 
remained  unehanged  since  the  commencement  of  the  glacial 
jieriod  would  have  been  an  incomparably  stronger  case,  for 
tliese  have  been  exposed  to  great  changes  of  climate  and  have 
migrated  over  great  distances  ;  whereas,  in  Egypt,  during  the 
last  3,000  years,  the  conditions  of  life,  as  far  as  we  know,  have 
remained  abs(jlutely  uniform.     The  fact  of  little  or  no  modifi- 


120  VARIOUS  OBJPX'TIOXS.  Chap.  IV. 

cation  liuviu^  bjcn  cficctcd  sinco  the  f^lacial  iicriocl  would  ha 
of  some  avail  ag'ainst  those  who  believe  iu  an  innate  and 
necessary  law  of  development,  l:)ut  is  powerless  against  the 
doctrine  of  natural  selection  or  the  survival  of  the  fittest,  which 
implies  only  that  variations  or  individual  differences  of  a  favor- 
able nature  occasionally  arise  in  a  few  s])ecies,  and  are  then 
preserved. 

It  has  been  objected,  if  natural  selection  be  so  powerful 
an  agent,  why  has  not  this  or  that  organ  been  modified  and 
improved?  Why  has  not  the  proboscis  of  the  hive-bee  been 
lengthened  so  as  to  reach  the  nectar  of  tlie  red-clover  ?  Why 
has  not  the  ostrich  acquired  the  power  of  llight  ?  But  grant- 
ing that  these  parts  and  organs  have  varied  in  the  right  direc- 
tion— granting  that  there  has  been  time  sufficient  for  the  slow 
work  of  natural  selection,  the  effects  being  often  checked,  as 
they  will  be  by  intercrossing  and  the  tendency  to  reversion, 
who  will  pretend  that  he  knows  the  life-history  of  any  one 
organic  being  sufficiently  well  to  say  that  any  particular  change 
would  be,  on  the  whole,  to  its  advantage  ?  Can  we  feel  sure 
that  a  long  proboscis  would  not  be  a  disadvantage  to  the  bive- 
bee  in  sucking  the  innumerable  small  flowers  which  it  fre- 
quents ?  Can  we  feel  sure  that  a  long  proboscis  would  not, 
by  correlation,  almost  necessarily  give  increased  size  to  other 
parts  of  the  mouth,  perhaps  interfering  with  the  delicate  cell- 
constructing  Avork?  In  the  case  of  the  ostrich,  a  moment's 
reflection  will  show  what  an  enormous  supply  of  food  would 
be  necessary  to  supply  force  for  this  bird  of  the  desert  to  move 
its  huge  body  through  the  air.  But  such  ill-considered  objec- 
tions are  hardly  worth  notice. 

The  celebrated  paleontologist,  Bronn,  at  the  close  of  his 
German  translation  of  this  work,  asks,  how,  on  the  principle 
of  natural  selection,  can  a  variety  live  side  by  side  with  the 
parent-species  ?  If  both  have  become  fitted  for  slightly-differ- 
ent habits  of  life  or  conditions,  they  might  live  together ; 
though,  in  the  case  of  animals  which  freely  cross  and  wander 
much  about,  varieties  seem  to  be  almost  always  confined  to 
distinct  localities.  But  if  we  put  on  one  side  polymorphic 
species,  in  which  the  variability  seems  to  be  of  a  peculiar  na- 
ture, and  all  mere  temporary  variations,  such  as  size,  albinism, 
etc.,  the  more  permanent  varieties  are  generally  fmmd,  as  far 
as  I  can  judge,  inhabiting  distinct  stations,  high  land  or  low 
land,  dry  or  moist  districts,  or  distinct  regions.  Bronn  also 
insists  that  distinct  species  never  differ  from  each  other  only 


Chap.  IV.  VAEIOUS  OBJECTIONS.  12^ 

ill  single  cliaractcrs,  ])ut  in  man}-  parts;  and  he  asks,  how  it 
comes  that  natural  selection  should  invariably  have  afrectcd 
simultaneously  many  parts  of  the  org'anization  i'  But  there  is 
not  the  loast  necessity  for  believing  that  all  the  parts  have  been 
simultaneously  modilied ;  they  may  have  been  gained  one  after 
the  other,  and  from  being  transmitted  together,  they  appeal 
to  us  as  if  simultaneously  formed.  Correlation,  however,  will 
account  for  various  parts  changing,  when  any  one  part  changes. 
We  have  e\'idence  of  this  in  our  domestic  races,  which,  though 
they  may  difl'er  greatly  in  some  one  selected  character,  always 
diller  to  a  certain  extent  in  other  characters. 

Bronn,  again,  asks  how  natural  selection  can  account  for 
dilTerences  between  species,  which  appear  to  be  of  no  service 
to  these  species,  such  as  the  length  of  the  ears  or  tail,  or  the 
folds  of  the  enamel  in  the  teeth,  of  the  several  species  of  hares 
and  mire  ?  With  respect  to  plants,  this  subject  has  been 
recently  discussed  by  Niigeli  in  an  admirable  essay.  He  admits 
that  natural  selection  has  effected  much,  but  he  urges  that  the 
families  of  plants  diil'er  chiefly  from  each  other  in  morphologi- 
cal characters,  which  seem  quite  imimportant  for  the  welfare 
of  the  species.  He  consequently  believes  in  an  innate  ten- 
dency toward  perfection  or  progressive  development.  He 
specifies  the  arrangement  of  the  cells  in  the  tissues,  and  of  the 
leaves  on  the  axis,  as  cases  in  which  natural  selection  Avould 
fail  to  act.  To  these  may  be  added  the  numerical  divisions 
in  the  parts  of  the  flower,  the  position  of  the  ovniles,  the  shape 
of  the  seed,  when  not  of  any  use  for  dissemination,  etc  Prof. 
Weismann,  in  discussing  Niigeli's  essay,  accounts  for  such  dif- 
f(!rences  by  the  nature  of  the  varying  organism  under  the  action 
of  certain  conditions ;  and  this  is  the  same  with  what  I  have 
called  the  direct  and  definite  action  of  the  conditions  of  lifo, 
causing  all  or  nearly  all  the  individuals  of  the  same  species  to 
vary  in  the  same  manner.  When  we  remember  such  cases  as 
the  formation  of  the  more  complex  galls,  and  certain  monstros- 
ities, which  cannot  be  accounted  for  l)y  reversion,  cohesion, 
etc.,  and  sudden  strongly-marked  deviations  of  structure,  such 
as  the  ajipearance  of  a  moss-roscj  on  a  connnon  rose,  we  must 
admit  that  the  organization  of  the  individual  is  capable  through 
its  own  laws  of  growth,  under  certain  conditions,  of  undergoing 
great  modifications,  independently  of  the  gradual  accumulation 
of  slight  inherited  modifications.  \'arious  morphological  differ- 
ences probably  come  under  this  head,  to  which  we  sliall  recur; 
but  many  differences  may  at  the  present  time  be  of  high  ser- 


128  VABIOUS  OBJECTIONS.  Cuaf.  IV. 

vice,  or  may  formerly  have  been  so,  although  >vc  arc  not  able 
to  perceive  their  use ;  and  these  will  have  been  acted  on  by 
natural  selection,  A  still  larger  number  of  mor}:)hological  dif- 
ferences may  certainly  be  looked  at  as  the  necessary  result — 
through  pressure,  the  withdrawal  or  excess  of  nutriment,  an 
early-formed  jiart  affecting  a  part  subsequently  developed,  cor- 
relation, etc. — of  other  adaptive  changes,  through  wliich  all 
species  must  have  j)assed  during  their  long  course  of  descent 
and  modilication. 

No  one  will  maintain  that  we  as  yet  know  the  uses  of  all 
the  pai-ts  of  any  one  plant,  or  the  functions  of  each  cell  in  any 
one  organ.  Five  or  six  years  ago,  endless  peculiarities  of 
structure  in  the  flowers  of  orchids,  great  ridges  and  crests,  and 
the  relative  positions  of  the  various  parts  AVould  have  been  con 
sidered  as  useless  moiphological  difl'erences  ;  but  now  we  know 
that  they  are  of  great  service,  and  must  have  been  under  the 
dominion  of  natural  selection.  No  one  at  present  can  explain 
Avhy  the  leaves  in  a  spire  diverge  from  each  other  at  certain 
angles ;  but  we  can  see  that  their  arrangement  is  related  to 
their  standing  at  equal  distances  from  the  leaves  on  all  sides ; 
and  we  may  reasonably  expect  that  the  angles  will  hereafter 
be  shown  to  follow  from  some  such  cause,  as  the  addition  of 
new  leaves  to  the  crowded  spire  in  the  bud,  as  inevitably  as 
the  angles  of  a  bee"'s  cell  follow  from  the  manner  in  which  the 
insects  work  together. 

In  certain  Avhole  groups  of  ])lants  the  ovules  stand  erect, 
and  in  others  they  are  suspended ;  and  in  some  few  plants 
within  the  same  ovarium  one  ovule  holds  the  former  and  a  sec- 
ond ovule  the  latter  position.  These  positions  seem  at  first 
purely  moi-jihological  and  of  no  physiological  signification ; 
but  Dr.  Hooker  informs  me  that,  of  the  ovules  within  the  same 
ovarium,  in  some  cases  the  upper  ones  alone  and  in  other  cases 
the  lower  ones  alone  are  fertilized ;  and  he  suggests  that  this 
probably  depcn^ls  on  the  direction  in  which  the  pollen-tubes 
enter.  If  so,  the  position  of  the  ovules,  even  when  one  is  erect 
and  the  other  suspended,  would  follow  from  the  selection  of  any 
slight  deviation  in  position  which  might  favor  their  fertilization 
and  the  production  of  seed. 

Several  plants  Ix'longing  to  distinct  orders  habitually  pro- 
duce flowers  of  two  kinds — the  one  open  and  of  the  orthnary 
structure,  the  other  closed  and  impM'fect.  In  the  latter  the 
l)etals  are  almost  alwaj-s  reductxl  to  the  merest  rudiments ;  the 
pollen-grains  are   reduced  in  diameter ;    five  of  the  alternate 


CnAP.  IV.  VARIOUS  OBJECTIONS.  log 

stamens  are  ruilimcntury  in  Ononis  columnas ;  and  in  some  spe- 
(•i(^s  of  Viola  three  stamens  arc  in  this  state,  two  retaining  their 
proper  fimction,  but  being'  of  very  small  size.  In  six  out  of 
lliirtv  of  tlie  closed  flowers  in  an  Indian  violet  (name  unknown, 
for  the  plants  have  not  as  yet  jiroduced  perfect  flowers),  the 
sepals  were  reduced  from  the  normal  lunnber  of  live  to  three. 
In  one  section  of  the  Malpighiacea3  the  closed  flowers,  according 
to  A.  de  Jussieu,  are  still  further  modified,  for  the  five  stamens 
which  stand  opposite  to  tlie  sepals  are  all  aborted,  a  sixth 
stamen  standhig  opposite  to  a  j)etal  being  alone  developed; 
and  this  stamen  is  not  present  in  the  ordinary  flowers  of  these 
species ;  the  style  is  aborted  ;  and  the  ovaria  are  reduced  froni 
three  to  two.  In  all  the  foregoing  plants  the  minute  closed 
flowers  are  of  high  service,  for  they  yield  with  perfect  seciu-ity, 
!Uid  with  the  expenditure  of  extremely  little  pollen,  or  other 
organized  matter,  a  large  supply  of  seed ;  while  the  perfect 
flowers  permit  occasional  crosses  with  distinct  individuals. 
Therefore,  these  changes  may  have  been,  and  no  doubt  have 
been,  efTi.'cted  through  natural  selection ;  and  I  may  add  that 
nearly  all  the  gradations  between  the  perfect  and  imperfect 
flowers  may  sometimes  be  observed  on  the  same  plant. 

With  respect  to  modifications  which  necessarily  follow  from 
other  cljangcs — through  the  withdrawal  or  excess  of  nutriment 
— througli  pressiu-e  and  other  unknown  influences — there  is 
space  here  only  for  a  few  brief  illustrations.  In  the  Spanish 
chestnut,  and  in  certain  fir-trees,  the  angles  of  divergence  of 
the  leaves  differ,  according  to  Schacht,  in  the  nearly  horizontal 
and  in  the  upright  branches.  In  the  common  rue  and  some 
other  plants,  one  flower,  usually  the  central  or  terminal  one, 
ojicns  first,  and  has  five  sepals  and  petals,  and  five  divisions  to 
the  ovarium  ;  while  all  the  other  flowers  on  the  plant  are  te- 
tramerous.  In  the  British  Adoxa  the  uppermost  flower  gener- 
ally has  two  cjilyx-lobes  with  the  other  organs  tetramerous, 
while  the  surrounding  flowers  generally  have  three  cal^'x-lobes 
with  the  other  organs  pentamerous  ;  and  this  difference  appears 
to  follow  from  the  manner  in  which  the  flowers  are  closely 
]>  icked  together.  In  many  Compositic  and  Umbellifera?,  and 
in  some  other  plants,  the  circumferential  flowers  have  their 
corollas  much  more  developed  tlian  those  of  the  centre;  and 
this  is  probably  the  result  of  natural  selection,  for  all  the 
flowers  are  thus  rendered  nuich  more  conspicuous  to  those  in- 
sects which  are  useful  or  even  neccs.sary  for  their  fertilization. 
In  connection  with  the  greater  development  of  the  corolla,  the 


130  VARIOUS  OBJECTIONS.  Chap.  IV. 

reproductive  organs  are  frequently  more  or  less  aborted.  It  is 
a  more  curious  fact  that  the  achenes  or  seeds  of  the  circum- 
ference and  of  the  centre  sometimes  differ  greatly  in  form, 
color,  and  other  characters.  In  Carthamus  and  some  othoi 
Composita^  the  central  achenes  alone  are  furnished  with  a  pap- 
pus ;  and  in  llyoseris  the  same  head  yields  achenes  of  three 
different  forms.  In  certain  Umbcllifeni:;  the  exterior  seeds,  ac- 
cording to  Tausch,  are  orthospermous,  and  the  central  one 
coelospermous,  and  this  difference  has  been  considered  by  De 
Candolle  as  of  the  highest  systematic  importance  in  the  family. 
If  in  such  cases  as  the  foregoing  all  the  leaves,  flowers,  fruits, 
etc.,  on  the  same  plant  had  been  subjected  to  precisely  the 
same  external  and  internal  conditions,  all  no  doubt  would  have 
presented  the  same  morjohological  characters  ;  and  there  clearly 
woiild  have  been  no  need  to  call  in  the  aid  of  the  principle  of 
progressive  development.  With  the  minute  closed  flowers,  as 
well  as  ^^^tll  many  degraded  parasitic  animals,  if  it  be  assumed 
that  any  such  aid  is  requisite,  we  sliould  have  to  call  in  an  in- 
nate tendency  to  retrogi-essive  development. 

]\Iany  instances  could  be  given  of  morphological  characters 
varying  greatly  in  plants  of  the  same  species  growing  close 
together,  or  even  on  the  same  individual  plant ;  and  some  of 
these  characters  are  considered  as  systematically  important. 
I  will  specify  only  a  few  cases  Avhich  have  first  occurred  to  me. 
It  is  not  necessary  to  give  instances  of  flowers  on  the  same 
plant  being  indifferently  tctramcrous,  pentamcrous,  etc.  ;  but 
as  when  the  parts  are  few,  numerical  variations  are  in  all  cases 
comparatively  rare,  I  may  mention  that,  according  to  De  Can- 
dolle, the  flowers  of  Papavcr  bracteatum  offer  two  sepals  with 
four  petals  (and  this  is  the  common  type  with  jioj^pies),  or 
three  se}>als  with  six  petals.  The  manner  in  which  the  petals 
are  folded  in  the  bud  is  in  most  groups  a  constant  morpho- 
logical character ;  but  Prof.  Asa  Gray  states  that  with  some 
species  of  Mimulus,  the  aestivation  is  almost  as  frequently  that 
of  the  Rhinanthidea3  as  c>f  the  Antirrhinidea?,  to  which  tribe 
the  genus  belongs.  Aug.  St.-Hilaire  gives  the  following  cases ; 
the  genus  Zanthoxylon  belongs  to  a  di\-ision  of  the  Kutacea3 
with  a  single  ovary,  but  in  some  of  the  species  flowers  may  bo 
found  on  the  same  plant,  and  even  in  the  same  panicle,  with 
cither  one  or  two  ovaries.  In  Helianthennnn  the  capsule  has 
been  described  as  unilocular  or  3-locular ;  and  in  H.  nuitabih^ 
"  Une  lame,  plus  ou  moins  large,  sY'tend  entre  le  pericarpe  et 
Ic  placenta."     In  the  flowers  of  Saponaria  ollicinalis,  Dr.  Mas- 


CiiAr.  IV.  VARIOUS   OBJECTlOiNS.  131 

tcrs  also  observed  instances  of  botli  mar<^inal  and  free  central 
placentation.  Lastl}',  St.-Hilaire  foinid  toward  the  southern 
extreme  of  the  ranfjc  of  Goniphia  oletvforniis  two  forms  which 
he  did  not  at  first  doubt  were  distinct  species,  but  he  subse- 
quently saw  them  g-rowinp^  on  the  same  bush ;  and  he  then 
adds,  "  A'oihl  done  dans  uu  memo  individu  des  lof^es  et  un 
style  qui  sc  rattachent  tantOt  il  un  axe  verticale  et  tantot  ;l  un 
gynobase." 

In  the  case  of  these  plants,  will  it  be  said  that  they  have 
been  detected  in  the  act  of  progTessin<T  toward  a  hijjher  state 
of  development  ?  On  the  contrary',  I  should  infer,  from  such 
characters  varying;'  so  f^reatly,  that  tliey  Avere  of  extremely 
small  importance  to  the  plants  themselves,  of  whatever  impoi-- 
tance  they  may  be  to  us  in  our  classifications.  Although  we 
are  quite  ipiorant  of  the  excitin<^  cause  of  each  modification, 
vet  it  st'cms  probaljle  from  what  we  know  of  the  relations  of 
varialjility  to  changed  conditions,  that  under  certain  conditions 
the  one  structure  Avould  have  prevailed  over  the  other,  and 
thus  might  have  been  rendered  almost  or  quite  constant. 
l'>om  th<?  very  fact  of  such  diflerences  being  unimportant  for 
the  welfare  of  the  species,  any  slight  dcAiations  which  did 
occur  Avould  not  be  augmented  or  accumulated  through  natural 
selection  ;  and  they  would  be  liable  to  obliteration  through  the 
occasional  intercrossing  of  distinct  individuals.  A  structure 
Avhich  has  hccn  developed  through  long-continued  selection, 
when  it  ceases  to  be  of  service  to  the  species,  will  generally 
become  variable,  as  we  see  with  rudimentary  organs ;  for  it 
will  no  longer  be  regulated  by  this  same  power  of  selection ; 
but  on  the  other  hand,  when  from  the  nature  of  the  organism 
and  from  a  change  in  the  conditions  definite  modifications  have 
been  produced  which  are  imimportant  for  the  welfare  of  the 
species,  they  may  be,  and  apparently  often  have  been,  trans- 
mitted in  nearly  the  same  state  to  numerous,  otherwise  modi- 
fied descendants.  Hair  has  been  transmitted  to  almost  all 
mammals,  feathers  to  all  birds,  and  scales  to  all  true  reptiles. 
A  structure,  whatever  it  may  be,  wiiich  is  common  to  many 
alli(Ml  forms,  is  ranked  by  us  as  of  high  systematic  importance, 
and  consequently  is  often  assimied  by  us  in  be  of  high  vital 
importance  to  tin*  species.  Thus,  as  I  am  inclined  to  believe, 
morphological  diilerenccs,  which  we  consider  as  important — 
such  as  the  arrangement  of  the  leaves,  the  divisions  of  the 
ovarium,  the  position  of  the  ovules,  etc. — first  appeared  in 
many   cases  as  fluctuating  variations,  which    sooner  or   later 


132  VARIOUS  OBJECTIONS.  Cn^r.  IV. 

became  almost  constant  tln-ough  the  nature  of  tlic  organism 
and  of  the  surrounding'  conditions,  as  Avell  as  through  inter- 
crossing ;  for  as  these  morphological  charactei'S  do  not  aflfect 
the  welfare  of  the  species,  any  slight  deviations  in  them  would 
not  be  acted  on  or  accumulated  through  natural  selection.  It 
is  a  strange  result  which  we  thus  arrive  at,  namely,  that  char- 
acters of  slight  vital  importance  to  the  species,  are  the  most 
important  to  the  systematist;  but,  as  we  shall  hereafter  see 
when  we  treat  of  the  genetic  principle  of  classification,  this  is 
by  no  means  so  paradoxical  as  it  at  first  appears.  Finally, 
whatever  may  be  thought  of  this  view,  in  none  of  the  forego- 
ing cases  do  the  facts,  as  far  as  I  can  judge,  afford  any  evi- 
dence of  the  existence  of  an  innate  tendency  toward  perfecti- 
bility or  progressive  development, 

I  need  allude  only  to  two  other  objections  :  a  distinguished 
botanist,  Mr.  H.  C.  ^\'atson,  behoves  that  I  have  overrated  the 
importance  of  divergence  of  character  (in  which,  however,  he 
apparently  believes),  and  that  convergence  of  character,  as  it 
may  be  called,  has  likewise  played  a  part,  Tliis  is  an  intricate 
subject  which  need  not  be  fully  discussed.  I  will  only  remark 
that  if  two  species  of  two  allied  genera,  both  produced  a  num- 
ber of  new  and  divergent  species,  I  can  believe  that  they 
might  sometimes  approach  each  other  so  closely  that  they 
would  for  convenience'  sake  be  classed  in  the  same  new  genus, 
and  thus  two  genera  would  converge  into  one ;  but  from  the 
strength  of  the  principle  of  inheritance,  and  from  the  two  par- 
ent-species already  differing  and  consequently  tending  to  vary 
in  a  somewhat  different  manner,  it  seems  hardly  credible  that 
the  two  new  groups  would  not  at  least  form  distinct  sections 
in  the  genus. 

Mr.  AVatson  has  also  objected  that  the  continued  action  of 
natui'al  selection  with  divergence  of  character  will  tend  to 
make  an  indefinite  number  of  specific  forms.  As  far  as  mere 
inorganic  conditions  are  concerned,  it  seems  probable  that  a 
sufficient  mmiber  of  species  would  soon  become  adapted  to  all 
considerable  diversities  of  heat,  moisture,  etc. ;  but  I  fully  admit 
that  the  mutual  relations  of  organic  beings  are  more  important ; 
and  as  the  number  of  species  in  any  country  goes  on  increas- 
ing, the  organic  conditions  of  life  become  more  and  more  com- 
plex. Conscquentl}'  there  seems  at  first  sight  no  limit  to  the 
amount  of  prolitaljle  diversification  of  structure,  and  therefore 
no  limit  to  the  number  of  species  wliich  might  be  })roduced. 
A\'e  do  not  know   that    even    the  most  prolific  area  is    fully 


CiiAr.  IV.  VARIOUS  OBJECTIONS.  I33 

stocked  with  specific  forms :  at  the  Cape  of  Good  Hope  and  in 
Australia,  which  support  such  an  astonishinnf  number  of  spe- 
cies, many  European  plants  have  become  naturalized.  But 
fj^coloiry  shows  us,  that  from  an  early  part  of  the  long'  tertiary 
jicriod  the  numljcr  of  species  of  shells,  and  that  from  the  mid- 
dle part  of  this  same  period  the  numlxT  of  mammals,  has  not 
greatly  or  at  all  increased.  AVhat,  tluMi,  checks  an  indefinite 
increase  in  the  number  of  species?  The  amount  of  life  (I  do 
ncjt  mean  the  lunnbcr  of  specific  forms)  supported  on  any  area 
nuist  have  a  limit,  depending;'  so  larj^ely  as  it  does  on  physical 
conditions ;  therefore,  if  an  area  be  inhabited  by  very  many 
species,  each  or  neaily  each  s})ecies  "will  be  represented  by  few 
individuals;  and  such  species  will  be  liable  to  extermination 
fiom  accidental  lluctuations  in  the  nature  of  the  seasons  or  in 
the  number  of  their  enemies.  The  process  of  extermination  in 
these  <;!ases  will  be  ra]>id,  whereas  the  production  of  new  spe- 
cies must  alwa3'S  be  slow.  Imac^inc  the  extreme  case  of  as 
many  species  as  individuals  in  England,  and  the  first  severe 
winter  or  A-ery  dry  summer  would  exterminate  thousands  on 
thousands  of  species.  Kare  species,  and  each  species  will  be- 
come rare  if  the  number  of  species  in  any  country  becomes 
indefinitely  increased,  will,  on  the  principle  often  explained, 
j)resent  within  a  given  period  few  favorable  variations;  conse- 
<|uently,  the  process  of  giving  birth  to  new  specific  forms  will 
thus  be  retarded.  When  any  species  becomes  very  rare,  close 
interbreeding  will  help  to  exterminate  it ;  authors  have  thought 
that  this  comes  into  play  in  accounting  for  the  deterioration  of 
the  Aurochs  in  Lithuania,  of  Ked  Deer  in  Scotland,  and  of 
liears  in  Norway,  etc.  Lastly,  and  this  I  am  inclined  to  think 
is  the  most  important  element,  a  dominant  species,  Avhich  has 
nlnMdy  beaten  many  competitors  in  its  own  home,  Avill  tend  to 
spread  and  supplant  many  others.  Alph.  de  Candolle  has 
shown  that  those  species  which  spread  widely  tend  generally  to 
spread  vcnj  widely  ;  and,  consequently,  they  will  tend  to  sup- 
|)lMnt  and  exterminate  several  species  in  several  areas,  and 
thus  check  the  inordinate  increase  of  specific  forms  throughout 
the  world.  Dr.  Hooker  has  recently  shown  that  in  the  south- 
east corner  of  Australia,  where,  apparently,  there  are  manv  in- 
vaders from  difTerent  quarters  of  the  world,  the  endemic  Aus- 
tralian species  have  been  greatly  reduced  in  number.  ITow 
nuich  weight  to  attribute  to  these  several  considerations  I  do 
not  jiretend  to  assign  ;  but  ronjointly  they  must  limit  in  each 
country  the  tendency  to  an  indefinite  augmentation  of  specific 
fonns. 


134  SUMMARY.  Chap.  IV. 

Sum)) tart/  of  Chcfpter. 

If  iiiulcr  changing  conditions  of  life  organic  beings  present 
individual  difiercnces  in  all  parts  of  their  structure,  and  this 
cannot  be  disputed  ;  if  there  bo,  owing  to  the  high  geometrical 
ratio  of  increase  of  each  species,  a  severe  struggle  for  life  at 
some  age,  season,  or  year,  and  tliis  certainly  cannot  be  disputed ; 
then,  considering  the  infinite  complexity  of  the  relations  of  all 
organic  beings  to  each  other  and  to  their  conditions  of  life, 
causing  an  infinite  diversity  in  structure,  constitution,  and 
habits,  to  be  advantageous  to  them,  it  would  be  a  most  extraor- 
dinary fact  if  no  variations  ever  occurred  useful  to  each  be- 
ing's OAvn  welfare,  in  the  same  inanner  as  so  many  variations 
have  occurred  useful  to  man.  /But  if  variations  useful  to  any 
organic  being  do  ever  occur,  assuredly  individuals  thus  charac- 
terized will  have  the  best  chance  of  being  preserved  in  the 
struggle  for  life  ;  and  from  the  strong  principle  of  inheritance, 
they  will  tend  to  produce  ofi'spring  similarly  characterized. 
This  principle  of  preservation,  or  the  survival  of  the  fittest,  I 
have  called  Natural  Selection^  It  leads  to  the  improvement 
of  each  creature  in  relation  to  its  organic  and  in  organic  condi- 
tions of  life ;  and  consequent]}',  in  most  cases,  to  what  must 
be  regarded  as  an  advance  in  organization.  Nevertheless,  low 
and  simple  forms  will  long  endure  if  well  fitted  for  their  simple 
conditions  of  life. 

Natural  selection,  on  the  principle  of  qualities  being  in- 
herited at  corresponding  ages,  can  modify  the  egg,  seed,  or 
young,  as  easily  as  the  adult.  Among  many  animals,  sexual 
selection  Avill  give  its  aid  to  ordinary  selection,  by  assuring  to 
the  most  vigorous  and  best  adapted  males  the  greatest  num- 
ber of  offspring.  Sexual  selection  will  also  give  characters  useful 
only  to  the  males,  in  their  struggles  with  other  males ;  and 
these  characters  Avill  be  transmitted  to  one  sex  or  to  both  sexes, 
according  to  the  form  of  inheritance  which  prevails. 

Whether  natural  selection  has  really  thus  acted  in  adapting 
the  various  forms  of  life  to  their  several  conditions  and  stations, 
must  be  judged  of  by  the  general  tenor  and  balance  of  the  evi- 
dence given  in  the  following  chapters.  But  we  already  see 
how  it  entails  extinction  ;  and  how  largely  extinction  has  acted 
in  the  world's  history,  geology  plainly  tleclarcs.  Natural  selec- 
tion, also,  leads  to  divergence  of  character ;  for  the  more  organic 
beings  diverge  in  structure,  habits,  and  constitution,  by  so  much 
can  a  greater  number  be  supported  on  the  same  area — of  which 


CiiAF.  IV.  SUMMARY.  I35 

we  see  proof  by  looking  to  the  inhabitants  of  any  small  spot 
or  (o  naturalized  productions.  Therefore,  durin>  the  modifica- 
tion of  the  descendants  of  anj-  one  species,  and  dm'in<>*  the  in- 
cessant stru^f^le  of  all  species  to  increase  in  numbers,  the  more 
diversified  these  descendants  become,  tlic  better  will  be  their 
chance  of  succccdinrr  in  the  battle  for  life.  Thus,  the  small 
dill'erences  distin<]^uishint^  varieties  of  the  same  species,  steadily 
tend  to  increase,  till  they  come  to  equal  the  greater  diflfereuces 
between  species  of  tlie  same  genus,  or  even  of  distinct  genera. 

We  have  seen  that  it  is  the  common,  the  widely-dilfused, 
and  widely-ranging  species,  belonging  to  the  larger  genera 
within  each  class,  which  vary  most;  and  these  tend  to  transmit 
((>  their  modified  offspring  that  superiority  which  now  makes 
them  dominant  in  their  own  countries.  Natural  selection,  as 
has  just  been  remarked,  leads  to  divergence  of  character  and  to 
much  Extinction  of  the  less  improved  and  intermediate  forms  of 
life.  On  these  principles,  the  nature  of  the  affinities,  and  the 
generally  AvoU-dellned  distinctions  of  the  innumerable  organic 
beings  in  each  class  througliout  the  Avorld,  may  be  explained. 
It  is  a  truly  wonderful  fact — the  wonder  of  M'hich  we  are  apt 
to  overlook  from  familiarity — that  all  animals  and  all  plants 
tliroughout  all  time  and  space  should  be  related  to  each  other 
in  natural  groups  subordinate  to  groups,  in  the  manner 
which  Ave  everywhere  behold — namely,  varieties  of  the  same 
species  most  closely  related  together  ;  species  of  the  same  genus 
less  closely  and  unequally  related  together,  forming  sections 
and  sub-genera ;  species  of  distinct  genera  much  less  closely 
related,  and  genera  related  m  difierent  degrees,  forming  sub- 
families, families,  orders,  sub-classes,  and  classes.  The  several 
subordinate  groups  in  any  class  cannot  be  ranked  in  a  single 
lile,  but  seem  rather  to  be  clustered  round  points,  and  these 
round  other  points,  and  so  on  in  almost  endless  cycles.  If 
each  species  has  been  independently  created,  no  explanation 
rm  be  given  of  this  great  fact  in  the  classification  of  all  organic 
beings;  but  it  is  explained  through  inheritance  and  tlie  com- 
plex action  of  natural  selection,  entailing  extinction  and  diver- 
gence of  character,  as  we  have  seen  illustrated  in  the  diagram. 

The  affinities  of  all  the  beings  of  the  same  class  have  some- 
limes  been  repres(Mited  by  a  great  tree.  I  believe  this  simile 
largely  speaks  (lie  trulli.  The  green  and  budding  twigs  may 
represent  existing  species  ;  and  those  produced  during  former 
years  may  represent  the  long  succession  of  extinct  species.  At 
each  period  of  growth   all   the   growing  twigs  have  tried  to 


133  SUMMARY.  CuAr.  IV. 

brancli  out  on  all  siili^s,  and  to  overtop  and  kill  the  surrounding 
t\vii>s  and  l)ranchcs,  in  the  same  manner  as  species  and  groups 
of  speeies  have  at  all  times  overmastered  other  species  in  the 
great  battle  for  life.  The  limbs,  di\'ided  into  great  branches, 
and  those  into  lesser  and  lesser  branches,  were  themselves  once, 
when  the  tree  Avas  small,  budding  twigs  ;  and  this  connec- 
tioTi  of  the  former  and  present  Inids  by  ramifying  branches  may 
well  represent  the  classification  of  all  extinct  and  living  species 
in  groups  subordinate  to  groups.  Of  the  many  twigs  which 
nourished  when  the  tree  was  a  mere  bush,  only  two  or  three, 
now  grown  into  great  branches,  yet  survive  and  bear  all  the 
other  branches ;  so  with  the  species  which  lived  during  long- 
])ast  geological  periods,  very  few  now  have  living  and  modified 
descendants.  From  the  first  growth  of  the  tree,  many  a  limb 
and  branch  has  decayed  and  dropped  off;  and  these  lost 
branches  of  various  sizes  may  represent  those  whole  orders, 
families,  and  genera,  which  have  now  no  living  representatives, 
and  whicli  are  known  to  us  only  from  being  found  in  a  fossil 
state.  As  we  here  and  there  see  a  thin,  straggling  branch 
sj)ringing  from  a  fork  low  down  in  a  tree,  and  which  by  some 
chance  has  been  favored  and  is  still  alive  on  its  summit,  so  we 
occasionally  see  an  animal  like  the  Ornithorh^mchus  or  Lepi- 
dosiren,  which  in  some  small  degree  connects  by  its  affinities 
two  large  branches  of  life,  and  which  has  apparently  been 
saved  from  fatal  competition  by  having  inhabited  a  protected 
station.  As  buds  give  rise  by  growth  to  fresh  buds,  and  these, 
if  vigorous,  branch  out  and  overtop  on  all  sides  many  a  feebler 
branch,  so  by  generation  I  believe  it  has  been  Avith  the  great 
Tree  of  Life,  which  fills  with  its  dead  and  broken  branches  the 
crust  of  the  earth,  and  covers  the  surface  with  its  ever-branch- 
inc:  and  beautiful  ramifications. 


Cu.vr.  V.  LAWS   OF  VARIATION.  IO7 


ciiArxER  y. 

LAWS    OF  VAUIATIOX. 

Effects  of clmntrofl  Coiuiillont'—T'iJo  and  Dis>nso,  combined  with  Natural  Selection; 
Orirtiiii  (if  Fliirlit  and  of  Vision— Acclimatization— Correlated  Variatiou— Com- 
pensation and  Keonoiny  of  (imwtli— False  C:orrclation» — Mnlti|)le,  Uudinicntary, 
and  l.iiwly-or^'anized  Stnietuies<  variable— Parts  developed  in  an  Unusual  Man- 
ner are  hij;ldy  variable  :  ?>poeific  Characters  more  variable  ttwn  Generic:  Second- 
ary Sexual  characters  variable— Species  of  the  t^anic  Genus  vary  in  au  analoguua 
llauucr— Ueverbioua  to  long-lost  Charactera — Sumaiary. 

.  I  HAVE  hitherto  sometimes  spoken  as  if  the  variations — so 
comn'ion  and  multilorin  with  org'anic  beings  nnder domestication, 
and  in  a  lesser  degree  with  those  in  a  state  of  nature — had 
l)een  due  to  cliance.  This,  of  course,  is  a  wholly  incorrect  ex- 
pression, but  it  serves  to  acknowledge  plainly  our  ignorance 
of  the  cause  of  each  particular  variation.  Some  authors  be- 
lieve it  to  be  as  much  the  function  of  the  reproductive  system 
to  produce  individual  difTerences,  or  slight  deviations  of  struc- 
tuie,  as  to  make  the  child  like  its  parents.  But  the  fact  of 
variations  and  monstrosities  occurring  much  more  frequently 
under  domestication  than  under  Nature,  and  the  greater  varia- 
l>ility  of  species  having  wide  ranges  than  of  those  having  re- 
stricted ranges,  lead  to  the  conclusion  that  variability  is  directly 
related  to  the  conditions  of  life  to  Avhich  each  species  has  been 
exposed  during  several  successive  generations.  In  the  first 
cliapter  I  attempt(>d  to  show  that  changed  conditions  act  in 
two  ways,  directly  on  the  whole  organization  or  on  certain 
])ar(s  alone,  jind  indirectly  through  the  reproductive  sj'stcm. 
Jn  all  cases  th(M-e  ate  two  factors,  the  nature  of  the  organism, 
which  is  nuich  the  most  important  of  the  two,  and  the  nature 
of  the  conditions.  The  direct  acticm  of  changed  conditions, 
leads  to  (h'Tmite  or  indefinite  results.  In  the  latter  case  the 
organization  seems  to  become  plastic,  and  we  have  nnich  fluc- 
tuating variability.  In  the  former  case  the  nature  of  the  or- 
ganism is  such  that  it  yields  readily,  when  subjected  to  cer- 
lain  conditions,  and  all,  or  nearly  all  the  individuals  become 
modified  in  the  same  way. 


l.iS  LAWS   OF  VARIATION.  Chap.  V. 

It  is  very  difficult  to  decide  how  far  clianii^cd  conditions, 
such  as  of  climate,  food,  etc.,  have  acted  in  a  definite  manner. 
There  is  some  reason  to  believe  that  in  the  course  of  time  the 
effects  have  been  greater  than  can  be  proved  to  be  the  case  by 
any  clear  evidence.  But  we  may  safely  conclude  that  the  in- 
niunerable  complex  coadaptations  of  structure  which  we  see 
throughout  Nature  between  various  organic  beings,  cannot  be 
attriljuted  simply  to  such  action.  In  the  following  cases  the 
conditions  seem  to  have  produced  some  slight  definite  effect : 
E.  Forbes  asserts  that  shells  at  their  southern  limit,  and  when 
living  in  shallow  water,  are  more  brightly  colored  than  those 
of  the  same  species  from  farther  north  or  from  a  greater  depth; 
but  these  statements  have  lately  been  disputed,  Mr.  Gould 
believes  that  birds  of  the  same  species  are  more  brightly  col- 
ored under  a  clear  atmosjihere,  than  when  living  on  islands  or 
near  the  coast ;  and  WoUaston  is  convinced  that  residence  near 
tlie  sea  affects  the  colors  of  insects.  Moquin-Tandon  gives  a 
li.st  of  plants  which  when  growing  near  the  sea-shore  have  their 
leaves  in  some  degree  ileshy,  though  not  elsewhere  fleshj'. 
Other  similar  facts  could  be  given. 

The  fact  of  varieties  of  one  species,  when  they  range  into 
the  habitations  of  other  species,  often  acquiring  in  a  slight 
degree  some  of  their  characters,  accords  Avith  the  view  that 
species  arc  only  well-marked  and  permanent  varieties.  Thus 
the  species  of  shells  Avhich  are  confined  to  tropical  and  shal- 
low seas  are  generally  brighter-colored  than  those  confined  to 
cold  and  deeper  seas.  The  birds  Avhich  are  confined  to  conti- 
nents are,  according  to  Mr.  Gould,  brighter-colored  than  those 
of  islands.  The  insect-species  confined  to  sea-coasts,  as  every 
collector  knows,  are  often  brassy  or  lurid.  Plants  which  live 
exclusively  on  the  sea-side  are  very  apt  to  have  Ileshy  leaves. 
He  who  believes  in  the  creation  of  each  species,  will  have  to 
say  that  this  insect,  for  instance,  was  created  of  a  brassy  color, 
because  it  was  intended  to  live  near  the  sea,  but  that  this  other 
insect  became  brassy  through  variation  as  soon  as  it  reached 
the  sea-coast. 

When  a  variation  is  of  the  slightest  use  to  any  being,  we 
cannot  tell  how  much  to  attribute  to  the  accumulative  action 
of  natural  selection,  and  how  much  to  the  definite  action  of  the 
conditions  of  life.  Tlius,  it  is  avcU  known  to  furriers  that  ani- 
mals of  the  same  species  have  thicker  and  better  fur  tlie  far- 
tlier  north  they  live  ;  but  who  can  tell  liow  much  of  this  dif- 
ference may  be  due  to  the  warmest-clad  individuals  having 


CiiAi-.  V.  EFFECTS  OF  USE  AND  DISUSE.  in<) 

1)ftM»  favored  and  preserved  during  many  generations,  and  how 
much  lo  the  action  of  tlie  severe  climate  ?  for  it  would  appear 
that  climate  has  some  direct  action  on  the  hair  of  our  domestic 
(juachupeds. 

Instances  could  be  given  of  similar  varieties  being  produced 
from  the  same  species  under  external  conditions  of  life  as  dif- 
ferent as  can  well  be  conceived ;  and,  on  the  other  hand,  of 
dissimilar  varieties  being  produced  imder  apparently  the  same 
external  conditions.  Again,  innumerable  instances  are  known 
to  ev(;ry  naturalist,  of  species  keeping  true,  or  not  varying  at 
all,  although  living  und<'r  the  most  opposite  climates.  Such 
considerations  as  these  incline  me  not  to  lay  much  weight  on 
the  direct  and  definite  action  of  the  conditions  of  life;  but  I 
fully  admit  that  strong  arguments  of  a  general  nature  may  be 
advanced  on  the  other  side. 

In  one  sense  the  conditions  of  life  may  be  said,  not  only  to 
cause  variability,  but  likewise  to  include  natural  selection  ;  for 
the  conditions  determine  whether  this  or  that  variety  shall  sur- 
yi\i.\  ]3ut  when  man  is  the  selecting  agent,  we  clearly  see 
that  the  two  elements  of  change  are  distinct ;  the  conditions 
cause  the  variability;  the  will  of  man,  acting  either  consciously 
or  unconsciously,  accumulates  the  variations  in  certain  direc- 
tions, and  tills  answers  to  the  survival  of  the  fittest  under 
nature. 

J^Jfects  of  Use  and  Disrise,  as  controlled  hy  Natural  Selection. 

From  the  facts  alluded  to  in  the  first  chapter,  I  think  there 
can  be  no  doubt  that  use  in  our  domestic  animals  strengthens 
and  enlarges  certain  parts,  and  disuse  diminishes  them  ;  and 
that  such  modifications  are  inherited.  Under  free  Nature,  we 
liave  no  standard  of  comparison,  by  which  to  judge  of  the 
elfecls  of  long-continued  use  or  disuse,  for  "we  know  not  the 
parent-fonns;  but  many  animals  have  structures  which-  can  be 
(•xi)lain<'d  by  the  efl'ects  of  disuse.  As  Prof.  Owen  has  remarked, 
llierc  is  no  greater  anomaly  in  Nature  than  a  bird  that  cannot 
l!y  ;  yet  there  are  several  in  this  state.  The  logger-headed  duck 
of  South  America  can  only  llap  along  the  surface  of  the  water, 
and  has  its  wings  in  nearly  the  same  condition  as  the  domestic 
Aylesbury  duck.  As  the  larger  ground-feeding  birds  seldom 
tak(>  fiight  except  to  escap<>  danger,  I  believe  that  the  nearly 
wingless  condition  of  several  birds,  which  now  inhabit  or  have 
lately  inhabited  several  oceanic  islands,  tenanted  by  no  beast 


140  EFFECTS  OF  USE  AND  DISL'SE.  Chap.  V. 

of  prey,  lias  been  caused  by  disuse.  The  ostricli,  indeed,  in- 
Imbils  continents  and  is  exposed  to  dann^er  from  -wliicli  it  cannot 
escape  by  llii^^lit,  but  by  kickinp^  it  can  defend  itself  from  ene- 
mies, as  well  as  any  of  the  smaller  ciuadrupeds,  "We  may  be- 
lieve that  the  progenitor  of  the  ostrich  fj^enns  had  habits  like 
those  of  a  bustard,  and  that,  as  natural  selection  increased  in 
successive  g-enerations  the  size  and  weight  of  its  body,  its  legs 
were  used  more,  and  its  wings  less,  until  they  became  incapa- 
ble of  flight. 

Kirby  has  remarked  (and  I  have  observed  the  same  fact) 
that  the  anterior  tarsi,  or  feet,  of  many  male  dung-feeding 
beetles  are  very  often  broken  off ;  he  examined  seventeen  spe- 
cimens in  his  own  collection,  and  not  one  had  even  a  relic  left. 
In  the  Onites  apclles  the  tarsi  are  so  habitually  lost,  that  the 
insect  has  been  described  as  not  having  them.  In  some  other 
genera  they  are  present,  but  in  a  rudimentary  condition.  In 
the  Ateuchus  or  sacred  beetle  of  the  Egyptians,  they  are  totally 
deficient.  The  evidence  that  accidental  mutilations  can  be  in- 
herited is  at  present  not  quite  decisive ;  but  the  remarkable 
case  observed  by  Brown-Sequard  of  inherited  epilepsy  in  guinea- 
pigs,  caused  by  an  operation  performed  on  the  spinal  cord, 
should  make  us  cautious  in  denying  such  power.  Hence  it 
Avill  ]>ei]iaps  be  safest  to  look  at  the  entire  absence  of  the  an- 
terior tarsi  in  Ateuchus,  and  their  rudimentary  condition  in 
some  other  genera,  as  due  to  the  effects  of  long-continued 
disuse;  for,  as  many  dung-feeding  beetles  are  generally  found 
with  their  tarsi  lost,  this  nnist  happen  earlv  in  life;  therefore 
tlie  tarsi  cannot  be  of  much  impoi'tance  or  be  nnich  used  by 
these  insects. 

In  some  cases  we  might  easily  put  do"^^'n  to  disuse  modifi- 
cations of  structure  which  are  wholly,  or  mainly,  due  to  natural 
selection.  Mr.  AYollaston  has  discovered  the  remarkable  fact 
that  ::300  beetles,  out  of  the  550  species  (but  more  are  now 
known)  which  inhabit  Madeira,  are  so  far  deficient  in  wings 
that  they  cannot  fly;  and  that,  of  the  twent^'-nine  endemic 
genera,  no  less  than  twenty-three  genera  have  all  their  species 
in  this  condition  !  Several  facts — namely,  that  beetles  in  many 
parts  of  the  world  are  frequently  blown  to  sea  and  perish  ; 
that  the  beetles  in  Madeira,  as  observed  by  Mr.  AVollaston,  lie 
much  concealed,  until  the  wind  lulls  and  the  sun  shines ;  that 
the  ])roportion  of  wingless  beetles  is  larger  on  the  exposed 
Desertas  than  in  Madeira  itself;  and  especially  the  extraor- 
dinary fact,  so  strongly  insisted  on  by  Mr.  AVoUaston,  of  the 


CiiAP.  V.  EFFECTS  OF  USE  AND  DISUSE.  141 

alino.st  entire  abs'jnco  of  certain  lar^jo  groups  of  beetles,  else- 
where excessively  numerous,  and  which  groups  have  ha])its  of 
life  almost  necessitating  frequent  flight — tliese  several  con- 
siderations have  made  me  believe  that  the  wingless  condition 
of  so  many  Madeira  beetles  is  mainly  due  to  the  action  of 
natural  selection,  but  combined  probably  with  disuse.  For 
during  many  successive  generations  each  individual  beetle 
which  Hew  least,  cither  from  its  wings  having  been  ever  so 
little  less  perfectly  developed  or  from  indolent  habit,  will  have 
had  the  best  chance  of  surviving  from  not  being  blown  out  to 
sea ;  and,  on  the  other  hand,  those  beetles  whicli  most  readily 
took  to  flight  would  oftenest  have  been  blown  to  sea  and  thus 
have  been  destroyed. 

The  insects  in  Madeira  which  arc  not  ground-feeders,  and 
which,  as  the  flower-feeding  coleoptera  and  lepidoptera,  must 
habilually  use  their  wings  to  gain  their  subsistence,  have,  as 
Mr.  Wuilaslon  suspects,  their  wings  not  at  all  reduced,  but 
even  elilarged.  This  is  quite  compatible  with  the  action  of 
natural  selection.  For  when  a  new  insect  first  arrived  on  the 
ishind,  the  tendency  of  natural  selection  to  enlarge  or  to  reduce 
the  wings,  would  depend  on  whether  a  greater  number  of  in- 
dividuals were  saved  by  successfully  battling  with  the  winds, 
or  by  giving  up  the  attempt  and  rarely  or  never  flying.  As 
wilh  mariners  shipwrecked  near  a  coast,  it  would  liave  been 
bcttiT  for  the  good  swimmers  if  they  had  been  able  to  swim 
still  farther,  whereas  it  would  have  been  better  for  the  bad 
swinnners  if  they  had  not  been  able  to  swim  at  all  and  had 
stuck  to  the  wreck. 

The  eyes  of  moles  and  of  some  burrowing  rodents  arc 
rudimentary  in  size,  and  in  some  cases  are  quite  covered  up  ])y 
skin  and  fur.  Tliis  state  of  the  eyes  is  probably  due  to  gradual 
reduction  from  disuse,  but  aided  perhaps  by  natural  selection. 
In  Soutli  America,  a  burrowing  rodent,  the  tuco-tuco,  or  Ctcn- 
omys,  is  even  more  subt(«rranean  in  its  habits  than  the  mole; 
.and  1  was  assured  by  a  Spaniard,  who  had  often  caught  them, 
that  th(»y  were  frequently  blind;  one  which  I  kept  alive  was 
certainly  in  this  condition,  the  cause,  as  appeared  on  dissection, 
having  been  inllammation  of  the  nictitating  membrane.  As 
frefjuent  inflammation  of  the  eyes  nnist  be  injurious  to  any 
animal,  and  as  eyes  are  certaiidy  not  necessary  to  aiiimals 
having  su])terranean  habits,  a  reduction  in  their  size,  with  the 
adhesion  of  the  eyelids  and  growth  of  fur  over  them,  might  in 


142  EFFECTS  OF  USE  AND  DISUSE.  Chap.  V, 

such  case  be  an  advantage ;  and  if  so,  natural  selection  would 
conslanlly  aid  the  efl'ects  of  disuse. 

It  is  well  known  that  several  animals,  belonging  to  the 
most  different  classes,  which  inhabit  the  caves  of  Carniola  and 
of  Kentucky,  are  blind.  In  some  of  the  crabs  the  foot-stalk  for 
tlie  eye  remains,  though  the  eye  is  gone ;  the  stand  for  the 
telescope  is  there,  though  the  telescope  with  its  glasses  has 
been  lost.  As  it  is  difficult  to  imagine  that  eyes,  though  use- 
less, could  be  in  any  way  injurious  to  animals  living  in  dark- 
ness, I  attribute  their  loss  wholly  to  disuse.  In  one  of  the 
bUnd  animals,  namely,  the  cave-rat  (Ncotoma),  two  of  which 
were  cajotured  by  Prof.  Silliman  at  above  half  a  mile  dis- 
tance fj-om  the  moutli  of  the  cave,  and  therefore  not  in  the 
profoundest  depths,  the  eyes  were  lustrous  and  of  large  size ; 
and  these  animals,  as  I  am  informed  by  Prof.  Silliman,  after 
having  been  exposed  for  about  a  month  to  a  graduated  light, 
acquired  a  dim  perception  of  objects. 

It  is  difficult  to  imagine  conditions  of  life  more  similar  tlian 
deep  limestone  caverns  imdcr  a  nearly  similar  climate  ;  so  that, 
on  the  common  view  of  the  blind  animals  haWng  been  sepa- 
rately created  for  the  American  and  European  caverns,  very 
close  similarity  in  their  organization  and  affinities  might  have 
been  expected.  This  is  certainly  not  the  case  if  we  look  at  the 
two  whole  faunas  ;  and,  with  respect  to  the  insects  alone, 
Schiodte  has  remarked  :  "  We  are  accordingly  prevented  from 
considering  the  entire  phenomenon  in  any  other  light  than 
something  purely  local,  and  the  similarity  which  is  exhibited 
in  a  few  forms  between  the  INIannnoth  Cave  (in  Kentucky)  and 
the  caves  in  Carniola,  otherwise  than  as  a  very  plain  expression 
of  that  analogy  which  subsists  generally  between  the  fauna  of 
Europe  and  of  North  America."  On  my  view  we  must  suppose 
that  American  animals,  having  in  most  cases  ordinary  powers  of 
vision,  slowly  migrated  by  successive  generations  from  the  outer 
world  into  the  deeper  and  deeper  recesses  of  the  Kentucky 
caves,  as  did  European  animals  into  the  caves  of  Europe.  We 
have  some  evidence  of  this  gradation  of  habit ;  for,  as  Schiodte 
remarks,  "  We  accordingly  look  upon  the  subterranean  faunas 
as  small  ramifications  which  have  penetrated  into  the  earth  from 
the  geograjihically  limited  faunas  of  the  adjacent  tracts,  and 
which,  as  they  extended  themselves  into  darkness,  have  been 
accommodated  to  surrounding  circumstances.  Animals  not  far 
remote  from  ordinary  forms,  proiwre  the  transition  from  light 
to  darkness.     Next  follow  those  that  are  constructed  for  twi- 


Chap.  V.  EFFECTS  OF  USE  AND   DISUSE.  I43 

li^lit ;  and,  last  of  all,  tlioso  destined  for  total  darkness,  and 
Aviiose  formation  is  (juitc  peculiar."  These  remarks  of  Schiiidte's, 
it  should  be  understood,  apply  not  to  the  same,  but  to  distinct 
species.  ]Jy  the  time  that  an  animal  had  reached,  after  num- 
berless generations,  the  deepest  recesses,  disuse  will  on  this 
view  have  more  or  less  perfectly  obliterated  its  eyes,  and 
natural  selection  will  often  have  ell'ected  other  changes,  such 
as  an  increase  in  the  length  of  the  antenmu  or  palpi,  as  a  com- 
pensation for  l)lindness.  Notwithstanding  such  modifications, 
we  might  expect  still  to  sec  in  the  cave-animals  of  America, 
allinities  to  tlie  other  inhabitants  of  that  continent,  and  in  those 
of  Europe  to  the  inhabitants  of  the  European  Continent.  And 
this  is  the  case  with  some  of  the  American  cave-animals,  as  I 
hi^ar  from  Prof.  Dana  ;  and  some  of  the  European  cave-insects 
arc  very  closely  allied  to  those  of  the  surroimding  countrv.  It 
woulil  be  most  dillicult  to  give  any  rational  explanation  of  the 
allinities  of  the  blind  cave-animals  to  the  other  inhabitants  of 
the  two  continents  on  the  ordinary  view  of  their  independent 
creation.  That  several  of  the  inhabitants  of  the  caves  of  the 
Old  and  New  Worlds  should  l)e  closely  related,  we  might  ex- 
pect from  the  Avell-knowu  relationship  of  most  of  their  other 
jiroductions.  As  a  blind  species  of  Bathyscia  is  found  in  abun- 
dance on  shady  rocks  far  from  caves,  the  loss  of  vision  in  the 
cave-species  of  this  one  genus  has  probably  had  no  relation  to 
its  dark  habitation  ;  and  it  is  very  natural  that  an  insect  al- 
ready deprived  of  vision  should  readily  become  adapted  to 
dark  caverns.  Another  blind  genus  (Anophthalmus)  offers 
this  remarkable  peculiarity:  the  several  distinct  species,  as  Mr. 
MuiTay  has  remarked,  iidiabit  several  distinct  European  caves 
and  likewise  those  of  Kentucky,  and  the  genus  is  found  no- 
v.here  except  in  caves ;  but  it  is  possible  that  the  progenitor 
or  progenitors  of  these  several  spec-ies,  while  furnished  with 
eyes,  formerly  may  have  ranged  widely  over  both  continents, 
and  then  have  become  extinct,  excepting  in  their  ])resent  se- 
cluded abodes.  Far  from  feeling  surprise  that  some  of  the 
rave-animals  should  be  very  anomalous,  as  Agassis  has  remarked 
in  regard  to  flu'  blind  fisli,  the  Amblyopsis,  and  as  is  the  case 
with  the  blind  I'rotcus  with  refertMice  to  the  reptiles  of  Europe, 
1  am  only  surprised  that  more  wrecks  of  ancient  HA;  have  not 
]>ccn  preserved,  owing  to  tin;  less  severe  competition  to  which 
the  inhabitants  of  these  daik  abodes  must  have  been  exposed. 


144  ACCLIMATIZATION.  Chat.  V. 

Acclimatization, 

Habit  is  hereditary  with  plants,  as  in  the  period  of  flower- 
iii<T,  in  the  amount  of  raui  requisite  for  seeds  to  germinate,  in 
the  time  of  sleep,  etc.,  and  tliis  leads  me  to  say  a  few  words  on 
acclimatization.  As  it  is  extremely  common  for  species  of  the 
same  genus  to  inhaljit  hot  and  cold  countries,  if  it  be  true  that 
all  the  species  of  the  sanic  g-cnus  are  descended  from  a  single 
parent-form,  acclimatization  must  be  readily  effected  during  a 
long  course  of  descent.  It  is  notorious  that  each  species 
is  adapted  to  the  climate  of  its  own  home :  species  from  an 
arctic  or  even  from  a  temperate  region  cannot  endure  a  tropical 
climate,  or  conversely.  So,  again,  many  succulent  plants  can- 
not endure  a  damp  climate.  But  the  degree  of  adaptation  of 
species  to  the  climates  under  which  they  live  is  often  overrated. 
We  may  infer  this  from  our  frequent  inability  to  predict 
whether  or  not  an  im})ortcd  plant  will  endure  our  climate,  and 
from  the  number  of  plants  and  animals  brought  from  different 
countries  which  are  here  perfectly  healthy.  We  have  reason 
to  believe  that  species  in  a  state  of  nature  are  closely  limited 
in  their  ranges  by  the  competition  of  other  organic  beings 
quite  as  much  as,  or  more  than,  by  adaptation  to  particular  cli- 
mates. But  whether  or  not  the  adaptation  be  generally  very 
close,  we  have  evidence,  in  the  case  of  some  few  plants,  of 
their  becoming,  to  a  certain  extent,  naturally  habituated  to 
diff(>rent  temperatures  ;  that  is,  they  become  acclimatized:  thus 
the  pines  and  rhododendrons,  raised  from  seed  collected  by  Dr. 
Hooker  from  the  same  species  gro^^^ng  at  different  heights  on 
the  Himalaya,  were  found  in  this  country  to  possess  different 
constitutional  powers  of  resisting  cold.  ^Ir.  Thwaites  informs 
me  that  he  has  observed  similar  facts  in  Ceylon ;  analogous 
observations  have  been  made  by  Mr.  H.  C.  Watson  on  Euro- 
pean species  of  plants  brought  from  the  Azores  to  England ; 
and  I  could  give  other  cases.  In  regard  to  animals,  several 
autlientic  instances  could  be  adduced  of  species  within  histori- 
cal times  having  largely  extended  their  range  from  warmer  to 
cooler  latitudes,  and  conversely  ;  but  we  do  not  positively  know 
tliat  these  animals  were  strictly  adapted  to  their  native  climate, 
though  in  all  ordinary  cases  we  assume  such  to  be  the  case ; 
nor  do  we  know  that  they  have  subsequently  become  specially 
acclimatized  to  their  new  homes,  so  as  to  be  better  fitted  for 
lliiMU  than  they  Avere  at  first. 

As  we  may  infer  that  our  domestic  animals  were  originally 


CiiAP.  V.  ACCLIMATIZATION.  Ii5 

chosen  by  uncivilized  nuin  because  they  ■were  useful^  and  be- 
cause they  bred  readily  inider  confinement,  and  not  because 
they  were  subsequently  found  cai)ablc  of  far-extended  trans- 
portation, the  common  and  extraordinary  capacity  in  our  do- 
mestic animals  of  not  only  withstandinf^  the  most  dillcrent 
climates,  but  of  beiii<T  perfectly  fertile  (a  far  severer  test)  under 
tliem,  may  be  used  as  an  argument  that  a  large  proportion  of 
other  animals  now  in  a  state  of  nature  could  easily  be  brought 
to  bear  widely-different  climates.  We  must  not,  however, 
push  the  foregoing  argument  too  far,  on  account  of  the  prob- 
able origin  of  some  of  our  domestic  animals  from  several  wild 
stocks  ;  the  blood,  for  instance,  of  a  tropical  and  arctic  wolf  or 
wild  dog  may  perhaps  be  mingled  in  our  domestic  breeds. 
The  rat  and  mouse  cannot  be  considered  as  domestic  animals, 
but  they  have  been  transported  by  man  to  many  parts  of  the 
world,  and  now  have  a  far  wider  range  than  any  other  rodent ; 
for  they,  live  under  the  cold  climate  of  Faroe  in  the  north  and 
of  the  Falklands  in  the  south,  and  on  many  islands  in  the  tor- 
rid zones.  Hence  adaptation  to  an}'  special  climate  may  be 
looked  at  as  a  quality  readily  grafted  on  an  innate  wide  ilexi- 
bility  of  constitution,  common  to  most  animals.  On  this  view, 
the  ca]iacity  of  enduring  the  most  different  climates  by  man 
himself  and  by  his  domestic  animals,  and  the  fact  of  the  extinct 
elephant  and  rhinoceros  ha\nng  formerly  endured  a  glacial  cli- 
mate, whereas  the  living  species  are  now  all  trojiical  or  sub- 
tropical in  their  habits,  ought  not  to  be  looked  at  as  anomalies, 
but  as  examples  of  a  very  common  flexibility  of  constitution, 
brought,  under  peculiar  circumstances,  into  action. 

How  much  of  the  acclimatization  of  species  to  any  peculiar 
climate  is  due  to  mere  habit,  and  how  much  to  the  natural  se- 
lection of  varieties  having  diilerent  innate  constitutions,  and 
how  much  to  both  means  combined,  is  an  obscure  question. 
Tliat  habit  or  custom  has  some  influence  I  nuist  believe,  both 
from  analogy  and  from  the  incessant  advice  given  in  agricul- 
tural works,  even  in  the  ancient  Encyclopicdias  of  China,  to  be 
very  cautious  in  trans])orting  animals  from  one  district  to 
another;  for  as  it  is  not  likely  that  man  should  have  succeeded 
in  selecting  so  many  breeds  and  sub-breeds  with  constitutions 
specially  fitted  for  their  own  districts,  the  result  nuist,  I  think-, 
be  due  to  habit.  On  the  other  hand,  natural  si^lection  would 
inevitably  tend  to  preserve  those  individuals  wliich  were  born 
with  constitutions  l)est  adapted  io  any  country  which  they  in- 
li  ibih'd.  In  treatises  on  many  kinds  of  cultivated  plants,  ccr- 
7 


146  CORKELATED  VARIATION.  Chap.  V. 

t:\in  varieties  are  said  to  withstand  certain  climates  better  than 
others ;  this  is  verv  strikingly  shown  in  works  on  fruit-trees 
published  in  the  United  States,  in  which  certain  varieties  are 
liabituallj  recommended  for  the  Northern  and  others  for  the 
Southern  States  ;  and,  as  most  of  these  vari(>tics  arc  of  recent 
origin,  they  cannot  owe  their  constitutional  differences  to  hab- 
it. The  case  of  the  Jerusalem  artichoke,  which  is  never  propa- 
gated in  England  by  seed,  and  of  which  consequently  new  va- 
rieties have  not  been  produced,  has  even  been  advanced — for 
it  is  now  as  tender  as  ever  it  was — as  proving  that  acclimatiza- 
tion cannot  be  effected !  Tlie  case,  also,  of  the  kidney-bean 
has  been  often  cited  for  a  similar  purpose,  and  with  much 
greater  weight;  but  until  some  one  will  sow,  during  a  score  of 
generations,  his  kidney-beans  so  early  that  a  very  large  pro- 
portion are  destroyed  by  frost,  and  then  collect  seed  from  the 
few  survivors,  with  care  to  prevent  accidental  crosses,  and  then 
again  get  seed  from  these  seedlings,  with  the  same  precau- 
tions, the  experiment  cannot  be  said  to  have  been  tried.  Nor 
let  it  be  supposed  that  differences  in  the  constitution  of  seed- 
ling kidney-beans  never  appear,  for  an  account  has  been  pub- 
lished how  much  more  hardy  some  seedlings  were  than  others; 
and  of  this  fact  I  have  myself  observed  striking  instances. 

On  the  whole,  I  think  we  may  conclude  that  habit,  or  use 
and  disuse,  have,  in  some  cases,  played  a  considerable  part  in 
the  modification  of  the  constitution,  and  of  the  structure  of 
various  organs ;  but  that  the  effects  of  use  and  disuse  have 
often  been  largely  combined  with,  and  sometimes  overmastered 
by,  the  natural  selection  of  innate  variations. 

Correlated  'Variation. 

I  mean  by  this  expression  that  the  whole  organization  is  so 
tied  together  during  its  growth  and  development,  that  when 
slight  variations  in  any  one  part  occur,  and  are  accumulated 
through  natural  selection,  other  parts  become  modified.  This 
is  a  very  important  subject,  most  imperfectly  understood,  and 
no  doubt  totally  different  classes  of  facts  may  be  here  easily 
confounded  together :  we  shall  presently  see  that  simple  in- 
heritance often  gives  the  false  appearance  of  correlation.  The 
most  obvious  instance  of  real  correlation  is,  that  variations  of 
structure  arising  in  the  young  or  in  the  larvae  naturally  tend 
to  affect  the  structin-e  of  the  mature  animal ;  in  the  same  man- 
ner as   ;my  malconfonnation  in  the   early  embryo   is   knoAvn 


Chap.  V.  CORRELATED  VAKIATION.  I47 

seriously  to  .ifFect  the  whole  org'anization  of  the  adult.  The 
several  parts  of  the  body  which  are  homolof^ous,  and  which, 
at  an  early  embryonic  period,  are  identical  in  structure,  and 
which  are  necessarily  exposed  to  similar  conditions,  seem  emi- 
nently liable  to  vary  in  a  like  manner:  we  see  this  in  the  right 
and  left  sides  of  the  body  varying  in  the  same  manner;  in  the 
front  and  hind  legs,  and  even  in  the  jaws  and  limbs,  varying 
together,  for  the  lower  jaw  is  believed  by  some  anatomists  to 
bs  homologous  with  the  limbs.  These  tendencies,  I  do  not 
doubt,  may  be  mastered  more  or  less  completely  by  natural 
selection :  thus  a  family  of  stags  once  existed  with  an  antler 
only  on  one  side ;  and  if  this  had  been  of  any  great  use  to  the 
breed,  it  might  probably  have  been  rendered  permanent  by 
selection. 

Homologous  parts,  as  has  been  remarked  by  some  authors, 
tend  to  cohere ;  this  is  often  seen  in  monstrous  plants :  and 
nothing  is  more  common  than  the  union  of  homologous  parts 
in  normal  structures,  as  the  imion  of  the  petals  of  the  corolla 
into  a  tube.  Hard  parts  seem  to  affect  the  forms  of  adjoining 
soft  parts ;  it  is  believed  by  some  authors  that  the  diversity  in 
the  shape  of  the  pelvis  in  birds  causes  the  remarkable  diver- 
sity in  the  shape  of  their  kidneys.  Others  believe  that  the 
shape  of  the  pelvis  in  the  human  mother  influences  by  pressure 
the  shape  of  the  head  of  the  child.  In  snakes,  according  to 
Schlegol,  the  shape  of  the  body  and  the  manner  of  swallowing 
determine  the  position  and  form  of  several  of  the  most  impor- 
tant viscera. 

The  nature  of  the  bond  of  correlation  is  frequently  quite 
obscure.  M.  Isidore  Geoffroy  St.-Hilaire  has  forcibly  remarked 
that  certain  malconformations  very  frequently,  and  that  others 
rarely  coexist,  without  our  being  able  to  assign  any  reason. 
^\''hat  can  be  more  singular  than  in  cats  the  relation  between 
complete  whiteness  with  blue  eyes  and  deafness,  or  between 
the  tortoise-shell  color  and  the  female  sex?  or  in  pigeons  be- 
tween their  feathered  feet  and  skin  betwixt  the  outer  toes,  or 
b;^tween  the  jiresence  of  more  or  less  down  on  the  young  birtl 
when  first  hatched,  with  the  future  color  of  its  plumage ;  or, 
again,  the  relation  between  the  hair  and  teeth  in  the  naked 
Turkish  dog,  though  here  no  doubt  homology  comes  into  play? 
With  respect  to  tliis  latter  case  of  correlation,  I  think  it  can 
hardly  be  accidental,  that,  if  we  pick  out  the  two  orders  of" 
mammals  which  are  most  abnormal  in  their  dermal  covering, 
viz.,  Cetacca  (whales)   and  Edentata   (amindilloes,  scaly  ant- 


148  CORRELATED  VARIATION.  Cuap.  V. 

eaters,  etc.),  these  are  likewise  the  most  abnormal  in  tlieir 
teeth. 

I  know  of  no  case  better  adapted  to  show  the  importance 
of  the  laws  of  variation  and  correlation,  independently  of  util- 
ity and  therefore  of  natural  selection,  than  that  before  referred 
to,  of  the  difference  between  the  outer  and  inner  flowers  in 
some  Conipositous  and  Umbelliferous  plants.  Every  one  knows 
the  dilTercnce  in  the  ray  and  central  florets  of,  for  instiuice,  th{^ 
daisy,  and  this  difference  is  often  accompanied  with  the  partial 
or  complete  abortion  of  the  rejoroductive  organs.  But  in  some 
of  these  plants,  the  seeds  also  differ  in  shape  and  sculpture. 
These  differences  have  been  attributed  by  some  authors  to  the 
I^rcssure  of  the  involucra  on  the  florets,  or  to  their  mutual  press- 
in-e,  and  the  shape  of  the  seeds  in  the  ray-florets  of  some  Com- 
positie  countenances  this  idea;  but  with  the  Umbellifene,  it 
is  by  no  means,  as  Dr.  Hooker  informs  me,  the  species  with 
the  densest  heads  Avhich  most  frequently  differ  in  their  inner 
and  outer  flowers.  It  might  have  been  tliought  that  the  de- 
velopment of  the  ray-pc^tals  by  drawing-  nourishment  from  the 
r(>productivc  organs  had  caused  their  abortion ;  but  this  can 
hardly  be  the  S(jle  cause,  for  in  some  Compositir;  the  seeds  of 
the  outer  and  inner  florets  differ  without  any  difference  in  the 
corolla.  Possibly  these  several  differences  may  be  connected 
Avith  the  diflcrent  flow  of  nutriment  toward  tlie  central  and 
external  flowers :  we  know,  at  least,  that,  with  normally  iireg- 
ular  flowers,  those  nearest  to  the  axis  are  most  subject  to 
jK'loria,  that  is,  they  become  S3'mmetrical.  I  may  add,  as  an 
instance  of  this,  and  of  a  striking  case  of  correlation,  that  I 
have  recently  observed  in  many  pelargoniums,  that  in  the  cen- 
tral flower  of  the  truss  the  two  upjier  petals  often  lose  their 
])atches  of  darker  color;  and  when  this  occurs,  the  adherent 
nectary  is  qviite  aborted.  When  the  color  is  absent  from  only 
one  of  the  two  upper  petals,  the  nectary  is  not  quite  aborted, 
but  is  much  shortened. 

With  respect  to  the  developmoit  of  the  corolla  in  the  cen- 
tral and  exterior  flowers,  Sprengel's  idea  that  the  ray-florets 
serve  to  attract  insects,  whose  agency  is  highly  advantageous 
or  necessary  for  the  fertilteation  of  these  plants,  is  highly  jirob- 
able ;  and  if  so,  natural  selection  may  have  come  into  i^lay. 
]>ut,  witli  respect  to  the  seeds,  it  seems  impossible  that  their 
diiVcrences  in  shape,  which  ai-e  not  ahvaj's  correlated  with  any 
difference  in  the  corolla,  can  be  in  any  way  beneficial :  yet  in 
the  Umbellifere  these  differences  arc  of  such  apparent  impor- 


riiAP.  V.  COMPENSATION  OF  GKOWTII.  149 

tiincc — the  seeds  bcinj^  sometimes  orlliospermons  in  tlic  exte- 
rior llowers  and  ca-lospennoiis  in  the  central  ilowors — that  the 
elder  iJe  Caiidollo  founded  his  main  divisions  in  the  order  on 
such  char;- -ters.  Hence,  as  before  remarked,  wc  see  that  modi- 
fications of  structure,  viewed  by  systematists  as  of  hi^h  value, 
may  be  AvlK)lly  due  to  the  laws  of  variation  and  correlation, 
without  beiuf^,  as  far  as  we  can  judf^e,  of  the  slightest  service 
t(^  the  species. 

We  may  often  falsely  attribute  fo  correlated  variation 
structures  which  arc  common  to  whole  groups  of  species,  and 
which  in  truth  arc  simply  due  to  inheritance :  for  an  ancient 
progenitor  may  have  acquired  through  natural  selection  some 
one  modification  in  structure,  and,  after  thousands  of  genera- 
tions, some  other  and  independent  modilication ;  and  these 
two  modiiications,  liaving  been  transmitted  to  a  whole  group 
of  descendants  witli  diverse  habits,  would  naturally  l^e  tlumght 
_to  be  correlated  in  some  necessary  manner.  Some  correlations 
are  apparently  due  to  the  manner  in  wliich  natural  selection 
acts.  For  instance,  Al]ih.  de  Candollc  has  remarked  that 
winged  seeds  are  never  found  in  fruits  wliich  do  not  open  :  I 
should  ex})lainthis  rule  by  the  impossiljility  of  seeds  gradually 
becoming  winged  through  natural  selection,  unless  the  ca])- 
sules  first  opened  themselves ;  for  in  this  case  alone  could  the 
seeds,  which  were  a  little  better  adapted  to  be  Avafted  by  the 
wind,  gain  an  advantage  over  those  less  well  fitted  for  wide 
dispersal. 

Compensation  and  Economy  of  Groxcth. 

llie  elder  GeoiTroy  and  Goethe  propounded,  at  about  the 
same  period,  their  law  of  compensation  or  balanccment  of 
growth  ;  or,  as  Goethe  expressed  it,  "  in  order  to  spend  on  one 
side,  Nature  is  forced  to  economize  on  the  other  side."  I  think 
this  holds  true  to  a  certain  extent  with  our  domestic  produc- 
tions: if  nourishment  flows  to  one  part  or  organ  in  excess,  it 
rarely  flows,  at  least  in  excess,  to  another  part;  thus  it  is  dif- 
ficult to  get  a  cow  to  give  nuicli  milk  and  to  fatten  readily. 
The  same  varieties  of  tlic  cabbage  do  not  yield  abundant  and 
luitritious  foliage  and  a  copious  supply  of  oil-bearing  seeds. 
When  the  seeils  in  our  fruits  become  atrophied,  tlie  fruit  itself 
gains  largely  in  size  and  quality.  In  our  poultry,  a  large  tuft 
of  feathers  on  the  head  is  generally  accompanied  by  a  dimin- 
ished comb,  and  a  large  beard  by  diminished  wattles.     With 


150  COMPENSATION  OF  GROWTU.  Chap.  V. 

species  in  a  state  of  nature  it  can  hardly  be  maintained  that 
the  law  is  of  universal  application  ;  but  many  jrood  observers, 
more  especially  botanists,  believe  in  its  truth.  I  will  not,  how- 
ever, here  give  any  instances,  for  I  see  hardly  any  way  of  dis- 
tinguishing between  the  effects,  on  the  one  hand,  of  a  part 
being  largel}'  developed  through  natural  selection  and  another 
and  adjoining  part  being  reduced  by  this  same  process  or  by 
disuse,  and,  on  the  other  hand,  the  actual  willidrawal  of  nutri- 
ment from  one  part  owing  to  the  excess  of  growth  in  another 
and  adjoining  part. 

I  suspect,  also,  that  some  cases  of  compensation  which  have 
been  advanced,  and  likewise  some  other  facts,  may  be  merged 
inider  a  more  general  principle,  namel}',  that  natural  selection 
is  continually  trying  to  economize  in  every  part  of  the  organ- 
ization. If  under  changed  conditions  of  life  a  structure  before 
useful  becomes  less  useful,  any  diminution,  however  slight,  in 
its  development,  Avill  be  seized  on  by  natural  selection,  for  it 
will  ]iroiit  the  individual  not  to  have  its  nutriment  wasted  in 
building  up  a  useless  structure.  I  can  thus  only  understand 
a  fact  with  which  I  was  much  struck  when  examining  cirri- 
pedes,  and  of  which  many  other  instances  could  be  given : 
namely,  that  when  a  cirripede  is  parasitic  within  another  and 
is  thus  protected,  it  loses  more  or  less  completely  its  own  shell 
or  carapace.  This  is  the  case  with  the  male  Ibla,  and  in  a 
truly  extraordinary  manner  with  the  Proteolepas  ;  for  the  car- 
apace in  all  other  cirripedes  consists  of  the  three  highly-impor- 
tant anterior  segments  of  the  head  enormously  developed,  and 
furnished  with  great  nerves  and  muscles ;  but  in  the  parasitic 
and  protected  Proteolepas,  the  whole  anterior  part  of  the  head 
i.s  reduced  to  the  merest  rudiment  attached  to  the  bases  of  the 
prehensile  antenna?.  Now  the  saving  of  a  large  and  complex 
structure,  when  rendered  superfluous  by  the  parasitic  habits  of 
the  Proteolepas,  though  effected  by  slow  steps,  would  be  a 
decided  advantage  to  each  successive  individual  of  the  species ; 
for  in  the  struggle  for  life  to  which  every  animal  is  exposed, 
each  individual  Proteolepas  would  have  a  better  chance  of 
supporting  itself,  by  less  nutriment  being  wasted  in  develop- 
ing a  structure  now  become  useless. 

Thus,  as  I  believe,  natural  selection  will  always  succeed  in 
the  long-run  in  reducing  and  saving  every  part  of  the  organi- 
zation, as  soon  as  it  is  rendered  by  changed  habits  of  life  super- 
fluous, without  by  any  means  causing  some  other  part  to  be 
largely  develojicd  in  a  corresponding  degree;  and,  converse- 


Chap.  V.  MULTIPLE  STKUCTUKES   VAKIABLE.  1.51 

ly,  that  natural  selection  may  perfectly  well  succeed  in  largely 
developing  any  organ,  without  requiring  as  a  necessary  com- 
pensation the  reduction  of  some  adjoinhig  part. 

Mullij)le,  liudimentaryy  and  Loichj-organized  Structures  are 

variable. 

It  seems  to  be  a  rule,  as  remarked  by  Is.  Geoffroy  St.-IIi- 
laire,  both  in  varieties  and  in  species,  that,  when  any  part  or 
organ  is  repeated  many  times  in  the  structure  of  the  same 
individual  (as  the  vertebnu  in  snakes,  and  the  stamens  in  poly- 
androus  ilowers),  tlie  number  is  variable;  whereas  the  number 
of  the  same  part  or  organ,  when  it  occurs  in  lesser  num])ers,  is 
constant.  The  same  author  and  some  botanists  have  further 
remarked  that  multiple  parts  are  also  very  liable  to  variation 
in  structure.  Inasmuch  as  this  "  vegetative  repetition,"  to  use 
Prof.  Owen's  expression,  seems  to  be  a  sign  of  low  organiza- 
tion, the  foregoing  remark  seems  connected  with  the  very  gen- 
eral opinion  of  Jiaturalists  that  beings  low  in  the  scale  of  Na- 
ture arc  more  variable  than  those  which  are  liigher.  I  pre- 
sume that  lowncss  in  this  case  means  that  the  several  parts  of 
the  organization  have  been  but  little  specialized  for  particular 
functions ;  and,  as  long  as  the  same  part  has  to  perform  diver- 
sified Avork,  wo  can  perhaps  see  Avhy  it  should  remain  variable, 
that  is,  why  natural  selection  should  not  have  preserved  or 
rejected  eacli  little  deviation  of  form  so  carefully  as  when  the 
part  had  to  serve  for  one  special  purpose  alone — in  the  same 
way  that  a  knife  which  has  to  cut  all  sorts  of  things  may  be  of 
almost  any  shape,  while  a  tool  for  some  particular  j^urpose 
had  better  be  of  some  particular  shape.  Natural  selection,  it 
should  never  be  forgotten,  can  act  on  each  part  of  each  being, 
solely  through  and  for  its  advantage. 

Kudimentary  parts,  it  has  been  stated  by  some  authors,  and 
I  believe  with  truth,  are  apt  to  be  highly  varialjle.  AVe  shall 
have  to  recur  to  tlie  general  subject  of  rudimentary  and  aborted 
organs;  and  I  will  here  only  add  tliat  tlieir  variability  seems 
to  be  owing  to  their  uselessness,  and  therefore  to  natiu-al  selec- 
tion having  no  power  to  check  deviations  in  their  structure. 
Thus  rudimentary  parts  are  left  to  the  free  play  of  the  various 
laws  of  growth,  to  the  effects  of  long-continued  disuse,  and  to 
tlic  tendency  to  reversion. 


152  UNUSUALLY  DEVELOPED  PARTS  Chap.  V. 

A  Part  developed  in  any  F^pccks  in  an  extraordinary  Degree 
or  Manner,  in  comparison  with  the  same  Part  in  allied 
JS^)ccic^,  tends  to  he  highly  variable. 

Several  years  ago  I  was  much  struck  by  a  rcmaik,  to  the 
above  effect,  made  by  Mr,  Waterliouse ;  Prof.  Owen,  also, 
seems  to  have  come  to  a  nearly  similar  conclusion.  It  is  hope- 
less to  attempt  to  convince  any  one  of  the  truth  of  the  aljovc 
j)roposition  witliout  giving  the  long  array  of  facts  which  I  have 
collected,  and  which  cannot  possibly  be  here  introduced.  I  can 
only  state  my  conviction  that  it  is  a  rule  of  high  generality. 
I  am  aware  of  several  causes  of  error,  but  I  hope  that  I  have 
made  due  allowance  for  them.  It  should  be  understood  that 
the  rule  by  no  means  applies  to  any  part,  however  unusually 
developed,  unless  it  be  unusually  developed  in  comparison  with 
the  same  part  in  closely-allied  species.  Thus,  the  wing  of  the 
bat  is  a  most  abnormal  structure  in  the  class  of  mammalia  ;  but 
the  rule  would  not  apply  here,  because  the  whole  group  of  bats 
possesses  wings ;  it  would  apply  only  if  some  one  species  had 
wings  develojoed  in  a  remarkable  manner  in  comparison  with 
other  species  of  the  same  genus.  The  rule  applies  very  strongly 
in  the  case  of  secondary  sexual  characters,  when  displayed  in 
any  unusual  manner.  The  term,  secondary  sexual  characters, 
used  by  Hunter,  applies  to  characters  which  are  attached  to 
one  sex,  but  are  not  directly  connected  Avith  the  act  of  repro- 
duction. The  nde  applies  to  males  and  females  ;  but  as  females 
more  rarely  offer  remarkable  secondary  sexual  characters,  it  ap- 
plies more  rarely  to  them.  The  rule  being  so  plainly  applicable 
in  the  case  of  secondary  sexual  characters,  may  be  due  to  the 
great  variability  of  these  characters,  whether  or  not  displayed 
in  any  unusual  manner — of  Avhich  fact  I  think  there  can  be 
little  doubt.  But  that  our  rule  is  not  confined  to  secondary 
sexual  characters  is  clearly  shown  in  the  case  of  hermaphrodite 
cirripedes ;  I  particularly  attended  to  ^Ir.  \Vaterhouse's  remark, 
while  investigating  this  order,  and  I  am  fully  convinced  that 
the  rule  almost  invariably  holds  good.  I  shall,  in  a  future; 
work,  give  a  list  of  all  the  more  remarkable  cases ;  I  will  lierc 
only  give  one,  as  it  illustrates  the  rule  in  its  largest  application. 
The  opercular  valves  of  sessile  cirripedes  (rock  barnacles)  are, 
in  every  sense  of  the  word,  very  important  structures,  and  they 
diller  extremely  little  even  in  different  genera  ;  but  in  the  several 
species  of  one  genus,  Pyrgoma,  these  valves  present  a  marvel- 
lous amount  of  diversification ;  the  homologous  valves  in  the 


CnAi-.  V.  HIGHLY  VARIABLE.  I.53 

different  species  beinp^  sometimes  wlioUy  unlike  in  shape;  and 
the  amount  of  variation  in  the  individuals  of  the  same  speciey 
is  so  great,  that  it  is  no  exaf^goration  to  state  that  the  varieties 
differ  more  from  each  other  in  the  characters  derived  from  these 
important  valves  than  do  other  species  belonging  to  distinct 
genera. 

As  birds  within  the  same  country  vary  in  a  remarkably 
small  degree,  I  have  jiarticuhu-ly  attended  to  them,  and  the 
rule  seems  to  me  certainly  to  hold  good  in  this  class.  I  cannot 
make  out  that  it  applies  to  plants,  and  this  would  seriously 
have  shaken  my  belief  in  its  truth,  had  not  the  great  variability 
in  plants  mad(;  it  jiarticularly  dillicult  to  compare  their  relative 
degrees  of  variabilit}'. 

When  we  see  any  part  or  organ  developed  in  a  remarkable 
degree  or  maimer  in  any  species,  the  fair  presumption  is,  that 
it  is  of  high  importance  to  that  species ;  nevertheless  it  is  in 
this  case  eminently  liable  to  variation.  Why  should  this  be 
so  ?  On  the  view  that  each  species  has  been  independently 
created,  with  all  its  ])arts  as  we  now  see  them,  I  can  see  no 
explanation.  But  on  the  view  that  groups  of  species  have 
descended  from  other  species,  and  have  been  modified  through 
natural  selection,  T  think  we  can  obtain  some  light.  First,  let 
me  remark  that  if  any  part  in  our  domestic  animals,  or  the 
whole  animal,  be  neglected  and  no  selection  be  applied,  that 
I)art  (for  instance,  the  comb  in  the  Dorking  fowl)  or  the  whole 
bref'd  will  cease  to  have  a  imiforin  character.  The  breed  will 
then  be  said  to  have  degenerated.  In  rudimentary  organs,  and 
in  tijose  which  have  been  but  little  specialized  for  an}''  partic- 
ular purpose,  and  perhaps  in  poljmiorphic  groups,  we  see  a 
nearly  parallel  natural  case;  for  in  such  cases  natural  selection 
either  has  not  or  cannot  have  come  into  full  play,  and  thus  the 
organization  is  left  in  a  fluctuating  condition.  But  what  here 
concerns  us  is,  that  those  points  in  our  domestic  animals,  whicli 
at  the  present  time  are  undergoing  rapid  change  by  continued 
selection,  are  also  eminently  liable  to  variation.  Look  at  the 
breeds  of  the  pigeon ;  see  what  a  prodigious  amount  of  differ- 
ence there  is  in  tht;  beaks  of  tumblers,  in  the  beaks  and  wattle 
of  carriers,  in  the  carriage  and  tail  of  fantails,  etc.,  these  being 
the  points  now  mainly  attiMided  to  by  Englisli  fanciers.  Even 
in  sub-breeds,  as  in  that  of  the  short-faced  tumbler,  it  is  notori- 
ously dillicult  to  breed  nearly  perfect  birds,  some  fre(|uently 
departing  widely  from  the  standard.  There  may  truly  be  said 
to  be  a  constant  struggle  going  on  between,  on  the  one  hand, 


15.4  UNUSUALLY  DEVELOPED  PARTS  Cnxr.  V. 

the  tendency  to  reversion  to  a  less  perfect  state,  as  well  as  an 
innate  tendency  to  fnrtlier  variability,  and,  on  the  other  hand, 
the  power  of  steady  selection  to  keep  the  breed  true.  In  the 
long'-run,  selection  gains  the  day,  and  we  do  not  expect  to  faU 
so  far  as  to  breed  a  bird  as  cf)arse  as  a  common  tumbler  from  a 
good  short-faced  strain.  Bnt  as  long  as  selection  is  rapidly 
going  on,  nnich  variability  in  the  parts  \mdergoing modification 
may  always  he,  expected.  It  further  deserves  notice  tliat  char- 
acters, modified  through  selection  by  man,  are  sometimes  trans- 
mitted, from  causes  quite  unknown  to  us,  more  to  one  sex  than 
to  the  other,  generally  to  the  male  sex,  as  with  the  wattle  of 
carriers  and  the  enlarged  crop  of  pouters. 

Now  let  us  turn  to  Nature.  AYlien  a  part  has  been  devel- 
oped in  an  extraordinary  manner  in  any  one  species,  compared 
with  the  other  species  of  the  same  genus,  we  may  conclude 
that  this  part  has  undergone  an  extraordinary  amount  of  modifi- 
cation since  the  period  when  the  species  branchetl  off  from  the 
connnon  progenitor  of  the  genus.  This  period  will  seldom  be 
remote  in  any  extreme  degree,  as  species  rarely  endure  for  more 
than  one  geological  period.  An  extraordinary  amovmt  of 
modification  implies  an  unusually  large  and  long-continued 
amount  of  variability,  which  has  continually  been  accumulated 
by  natural  selection  for  the  benefit  of  the  species.  But  as  the 
variability  of  the  extraordinarily  developed  part  or  organ  has 
■];)een  so  great  and  long-continued  within  a  period  not  exces- 
sively remote,  Ave  might,  as  a  general  rule,  still  expect  to  find 
more  A-ariability  in  such  parts  than  in  otlier  parts  of  the  organi- 
zation which  have  remained  for  a  much  longer  period  nearly 
constant.  And  this,  I  am  convinced,  is  the  case.  Tliat  the 
struggle  between  natural  selection  on  the  one  hand,  and  the 
tendency  to  reversion  and  variability  on  the  other  hand,  will  in 
the  course  of  time  cease ;  and  that  the  most  abnormally  devel- 
oped organs  may  be  made  constant,  I  see  no  reason  to  doubt. 
Ilence,  when  an  organ,  however  abnormal  it  may  be,  has  been 
transmitted  in  approximately  the  same  condition  to  many  modi- 
fied descendants,  as  in  the  case  of  the  wing  of  the  bat,  it  must 
have  existed,  according  to  my  theory,  for  an  immense  period 
in  nearly  the  same  state;  and  thus  it  comes  to  be  no  more  vari- 
al)le  than  any  other  structure.  It  is  only  in  those  cases  in 
wliich  the  modification  has  been  comparatively  recent  and 
extraordinarily  great  that  we  ought  to  find  i\\o  generative  vari- 
(ihllitij^  as  it  may  be  called,  still  present  in  a  high  degree.  For 
in  this  case  tlie  variability  will  seldom  as  yet  have  been  fixed 


Chap.  V.  HIGHLY  VARIABLE.  I55 

by  the  continued  selection  of  the  individuals  varj-ing  in  the 
•required  manner  and  degree,  and  by  the  continued  rejection 
of  those  tending  to  revert  to  a  former  and  less-modified  con- 
dition. 


Si'iecific  Characters  more  variable  than   Generic  Characters^ 

The  principle  included  in  the  above  remarks  may  be  ex- 
tended. It  is  notorious  that  specific  characters  are  more  va- 
riable than  generic.  To  exjilain  by  a  simple  example  -what  is 
meant :  If  in  a  large  genus  of  jilants  some  species  had  blue 
flowers  and  some  had  red,  the  color  Avould  be  only  a  specific 
character,  and  no  one  "would  be  surprised  at  one  of  the  blue 
species  varying  into  red,  or  conversely ;  but  if  all  the  species 
had  blue  ilowers,  the  color  would  become  a  generic  character, 
and  its  variation  Avould  be  a  more  unusual  circumstance.  I 
liave  chosen  this  example  because  an  explanation  is  not  in  this 
case  applicable,  which  most  naturalists  would  advance,  namely, 
that  specific  characters  are  more  variable  than  generic,  because 
they  are  taken  from  parts  of  less  physiological  importance  than 
those  commonly  used  for  classing  genera.  I  believe  this  ex- 
planation is  partly,  yet  only  indirectly,  true  ;  I  shall,  however, 
have  to  return  to  this  subject  in  the  cliapter  on  Classification. 
It  would  be  almost  superfluous  to  adduce  evidence  in  support 
of  the  a])ove  statement,  that  specific  characters  are  more  va- 
riable than  generic  ;  but  I  have  repeatedly  noticed  in  Avorks  on 
natural  history,  that,  when  an  author  has  remarked  with  sur- 
prise that  some  imjiortant  organ  or  part,  which  is  generally 
very  constant  throughout  large  groups  of  species,  has  differed 
considerably  in  closelj'-allied  species,  it  has  also  been  vari- 
able in  the  individuals  of  some  of  the  species.  And  this  fact 
shows  that  a  character,  Avhicli  is  generally  of  generic  value, 
when  it  sinks  in  value  and  becomes  only  of  specific  value,  often 
becomes  variable,  though  its  physiological  importance  may  re- 
main the  same.  Something  of  the  same  kind  applies  to  mon- 
strosities :  at  least  Is.  GeoflVoy  St.-Hilaire  seems  to  entertain 
no  doubt  that  the  more  an  organ  normally  differs  in  the  differ- 
ent species  of  the  same  group,  the  more  subject  it  is  to  indi- 
vidual anomalies. 

On  the  ordinary  view  of  each  species  having  been  inde- 
pendently created,  why  should  that  part  of  the  structure, 
which  differs  from  the  same  part  in  other  independently-created 
species  of  the  same  genus,  be  more  variable  than  those  parts 


156  SECONDARY  SEXUAL  Chap.  V. 

which  are  closely  alike  in  the  several  species?  I  do  not  sec 
that  any  explanation  can  be  given.  But  on  the  vie'.v  that  spe- 
cies are  only  stron2;ly  marked  and  fixed  varieties,  Ave  might  ex- 
pect to  find  them  still  oil  en  continuing  to  vary  in  those  parts 
of  their  structure  which  had  varied  witliin  a  moderately-recent 
period,  and  which  had  thus  come  to  diCfer,  Or,  to  state  the 
case  in  another  manner :  The  points  in  which  all  the  species 
of  a  genus  resemble  each  other,  and  in  ■which  they  differ  from 
allied  genera,  are  called  generic  characters ;  and  these  charac- 
ters in  common  I  attribute  to  inheritance  from  a  common  pro- 
genitor, for  it  can  rarely  have  happened  that  natural  selection 
Avill  have  modified  several  species,  fitted  to  more  or  less  wide- 
ly-diflerent  habits,  in  exactly  the  same  manner :  and  as  these 
so-called  generic  characters  have  been  inherited  from  before 
tlie  period  when  the  different  species  first  branched  off  from 
their  common  progenitor,  and  subsequently  have  not  varied  or 
come  to  differ  in  any  degree,  or  only  in  a  slight  degree,  it  is 
not  probaljle  that  tliey  should  vary  at  the  present  day.  On  the 
other  hand,  the  points  in  which  species  differ  from  other  spe- 
cies of  the  same  genus  are  called  specific  characters ;  and  as 
these  specific  characters  have  varied  and  come  to  differ  since 
tlie  period  when  the  species  branched  off  from  a  common  pro- 
genitor, it  is  probable  that  they  should  still  often  be  in  some 
degree  variable — at  least  more  variable  than  those  parts  of  the 
organization  which  have  for  a  very  long  period  remained  con- 
stant. 

Secondary  Sexual  Characters  variable. 

In  coimection  with  the  present  subject,  I  Avill  make  only 
two  other  remarks.  I  think  it  will  be  admitted,  without  my 
entering  on  details,  that  secondary  sexual  characters  are  very 
variable;  I  think  it  also  will  be  admitted  that  species  of  the 
same  group  diller  from  each  other  more  widely  in  their  second- 
ary sexual  characters  tlian  in  other  parts  of  their  organization; 
(^ompare,  for  instance,  tlie  amount  of  difference  between  the 
males  of  gallinaceous  birds,  in  which  secondary  sexual  charac- 
ters are  strongly  displayed,  with  the  amount  of  difference  be- 
tween the  females;  and  the  tnith  of  tliis  jiroposition  will  be 
granted.  Tiie  cause  of  the  original  variability  of  secondary 
S(\xual  characters  is  not  manifest ;  but  we  can  see  why  these 
characters  should  not  have  been  rendered  as  constant  and  imi- 
form  as  other  parts  of  the  organization;  for  secondary  sexual 
characters  have  been  accumulated  by  sexual  selection,  which  is 


Chap.  V.  CHARACTERS  VARIABLE.  157 

less  rigud  in  its  action  tlian  ordinary  selection,  as  it  does  not 
entail  death,  bnt  only  gives  fewer  offspring  to  the  less  favored 
males.  Whatever  tlie  cause  may  be  of  the  variability  of  sec- 
ondary sexual  characters,  as  they  are  highly  variable,  sexual  se- 
lection, will  have  had  a  wide  scope  for  action,  and  may  thus 
readily  have  succeeded  in  giving  to  the  species  of  the  same 
group  a  greater  amount  of  difference  in  their  sexual  characters 
tlian  in  other  parts  of  their  structure. 

It  is  a  remarkable  fact  that  the  secosdary  sexual  differ- 
ences between  the  two  sexes  of  the  same  sjiecies  arc  generally 
displayed  in  the  very  same  parts  of  the  organization  in  whicli 
the  different  species  of  the  same  genus  dilfer  from  each  other. 
Of  this  fact  I  will  give  two  instances  in  illustration,  the  first 
which  hap])en  to  stand  on  my  list;  and,  as  the  differences  in 
these  cases  are  of  a  very  unusual  nature,  the  relation  can  hard- 
ly be  accidental.  The  same  number  of  joints  in  the  tarsi  is  a 
character  generally  common  to  very  large  gi-oups  of  beetles, 
but  in  the  Engid:e,  as  Westwood  has  remarked,  the  number 
varies  greatly;  and  the  number  likewise  differs  in  the  two 
sexes  of  the  same  species  :  again,  in  fossorial  liymenoptera,  the 
manner  of  neuration  of  the  wings  is  a  character  of  the  highest 
importance,  because  common  to  large  groups  ;  but  in  certain 
genera  the  ncin-ation  differs  in  the  different  species,  and  like- 
wise in  the  two  sexes  of  the  same  species.  Sir  J.  Lubbock 
has  recently  remarked  that  several  minute  crustaceans  offer  ex- 
cellent illustrations  of  this  law.  "  In  Pontella,  for  instance, 
the  sexual  characters  arc  afforded  mainly  l)y  the  anterior  an- 
tenna) and  by  the  fifth  pair  of  legs  :  the  specific  differences 
also  are  principally  given  by  these  organs."  This  relation  has 
a  clear  meaning  on  my  view  of  the  subject :  I  look  at  all  th(! 
species  of  the  same  genus  as  ha^nng  as  certainly  descended 
from  the  same  progenitor  as  have  the  two  sexes  of  any  one  of 
the  species.  Conseijuently,  whatever  part  of  the  structure  of 
the  common  progenitor,  or  of  its  early  descendants,  became 
A-ariable,  variations  of  this  part  Avould,  it  is  highly  jiroljable,  be 
taken  advantage  of  by  natural  and  sexual  selection,  in  order  to 
fit  the  several  species  to  their  several  j)lac(\s  in  the  economy  of 
Nature,  and  likewise  to  fit  the  two  sexes  of  the  same  S]iecies  to 
each  other,  or  to  fit  the  males  and  females  to  different  habits  of 
life,  or  the  males  to  struggle  with  other  males  for  the  jiosses- 
sion  of  the  females. 

Finally,  then,  I  conclude  that  the  greater  variability  of 
specific    characteis,  or   those   which  distinguish  species  from 


158  DISTINCT  SPECIES  PRESENT  Chap.  V. 

species,  ihan  of  generic  characters,  or  those  which  the  species 
possess  in  roinmon ;  that  the  frequent  extreme  variability  of 
any  part  which  is  developed  in  a  species  in  an  extraordinary 
manner  in  comparison  with  the  same  part  in  its  congeners ; 
and  the  slight  degree  of  variability  in  a  part,  however  extraor- 
dinarily it  may  be  developed,  if  it  be  common  to  a  whole  group 
of  species ;  that  the  great  variability  of  secondarj'  sexual  char- 
acters, and  the  great  amount  of  difference  in  these  same  char- 
acters between  closely-allied  species ;  that  secondary  sexual 
and  ordinary  specific  differences  are  generally  displayed  in  the 
same  parts  of  the  organization — are  all  principles  closely  con- 
nected together.  All  being  mainly  due  to  the  species  of  the 
same  group  having  descended  from  a  common  progenitor,  from 
whom  they  have  inherited  much  in  common — to  parts  whicli 
have  recently  and  largely  varied  being  more  likely  still  to  go 
on  varying  than  parts  which  have  long  been  inherited  and 
have  not  varied — to  natural  selection  having  more  or  less  com- 
pletely, according  to  the  lapse  of  time,  overmastered  the  ten- 
dency to  reversion  and  to  further  variability — to  sexual  selec- 
tion being  less  rigid  than  orchnary  selection — and  to  variations 
in  the  same  parts  having  been  accumulated  by  natural  and 
sexual  selection,  and  having  been  thus  adapted  for  secondary 
sexual,  and  for  ordinary  purposes. 

Distinct  Species  present  analogous  Variations  ;  and  a  Variety 
of  one  Species  often  assumes  some  of  the  Characters  of  an 
allied  Species,  or  reverts  to  soyne  of  the  Characters  of  an 
early  Progenitor. 

These  propositions  will  be  most  readily  understood  by  look- 
ing to  our  domestic  races.  The  most  distinct  breeds  of  pigeons, 
in  countries  most  widely  apart,  present  sub-varieties  with  re- 
versed feathers  on  the  head  and  feathers  on  the  feet — charac- 
ters not  possessed  by  the  aboriginal  rock-pigeon ;  these,  then, 
are  analogous  variations  in  two  or  more  distinct  races.  The 
frequent  presence  of  fourteen  or  even  sixteen  tail-feathers  in  the 
pouter  may  be  considered  as  a  variation  representing  the  nor- 
mal structure  of  another  race,  the  fantail.  I  presume  that  no 
one  will  doubt  that  all  such  analogous  variations  are  due  to  the 
several  races  of  the  pigeon  having  inherited  from  a  common 
]>arent  the  same  constitution  and  tendency  to  variation,  when 
acted  on  bv  similar  unknown  influences.  In  the  vegetable 
kingdom  we  have  a  case  of  analogous  variation  in  the  enlarged 


Chap.  V.  ANALOGOUS  VARIATIONS.  I59 

stems,  or  roots  as  commonly  called,  of  the  Swedish  turnip  and 
Ruta-ba^'a,  })hmts  wliich  several  botanists  rank  as  varieties 
produced  by  cultivation  from  a  common  parent;  if  this  be  not 
so,  the  case  will  then  be  one  of  analogous  variation  in  two  so- 
called  distinct  species  ;  and  to  these  a  third  may  be  added, 
namely,  the  common  turnip.  AccoriUng  to  the  ordinary  view 
of  each  species  having  be(?n  independently  created,  we  should 
have  to  attribute  this  similarity  in  the  enlarged  stems  of  these 
three  plants,  not  to  the  vera  causa  of  community  of  descent, 
and  a  consequent  tendency  to  vary  in  a  like  manner,  but  to 
three  separate  yet  closely-related  acts  of  creation.  Many  simi- 
lar cases  of  analogous  variation  have  been  observed  by  Naudin 
in  the  great  gourd-family,  and  by  various  authors  in  oiu*  cereals. 
Similar  cases  occurring  with  insects  under  their  natural  con- 
ditions have  lately  been  discussed  with  much  al)ility  by  Mr. 
Walsh,  who  has  grouped  theni  under  his  law  of  Equable  Va- 
riability. 

With  pigeons,  however,  we  have  another  case,  namely,  the 
occasional  appearance  in  all  the  breeds  of  slaty-blue  birds  with 
two  black  bars  on  the  v/ings,  white  loins,  a  bar  at  the  end  of 
the  tail,  with  the  outer  feathers  externally  edged  near  their 
bases  with  white.  As  all  these  marks  are  characteristic  of  the 
parent  rock-pigeon,  I  presume  that  no  one  will  doubt  that  this 
is  a  case  of  reversion,  and  not  of  a  new  yet  analogous  variation 
appearing  in  the  several  breeds.  ^Ve  may,  I  think,  confidently 
come  to  tliis  conclusion,  because,  as  we  have  seen,  these  colored 
marks  are  eminently  liable  to  appear  in  tlie  crossed  oflsining 
of  two  distinct  and  differently-colored  breeds;  and  in  this  case 
there  is  nothing  in  the  external  conditions  of  life  to  cause  tlie 
reappearance  of  the  slaty-blue,  with  the  several  marks,  beyond 
the  influence  of  the  mere  act  of  crossing  on  the  laws  of  inher- 
itance. 

No  doubt  it  is  a  very  surprising  fact  that  characters  should 
reappear  after  having  lieen  lost  for  many,  probably  for  hun- 
dreds of  generations.  But  when  a  ])reed  has  been  crossed  only 
once  by  some  otlier  breed,  the  offspring  occasionally  show  a 
tendency  to  revert  in  character  to  the  foreign  breed  for  many 
generations — some  say  for  a  dozen  or  even  a  score  of  genera- 
tions. After  twelve  general i(ms,  the  proportion  of  blood,  to 
use  a  common  expression,  of  any  one  ancestor,  is  only  1  in 
3,048 ;  and  yet,  as  we  see,  it  is  generally  believed  that  a  ten- 
dency to  reversion  is  retained  by  tliis  very  small  projiortion  of 
foreign  blood.     In  a  breed  which  has  not  been  crossed,  but 


IGO  DISTINCT  SPECIES  PRESENT  Chap.  V. 

in  which  both  parents  liave  lost  some  character  which  ilieir 
progenitor  possessed,  the  tendency,  Avliether  stronf^  or  -weak, 
to  reproduce  the  lost  character  might  be,  as  was  formerly  re- 
marked, for  all  that  wc  can  sec  to  the  contrary,  transmitted 
for  almost  any  uuml:)cr  of  generations.  When  a  character  which 
h;is  been  lost  in  a  lu'ced,  reappears  after  a  gTcat  immber  of 
generations,  the  most  probable  hypothesis  is,  not  that  the  ofl- 
spring  suddenly  takes  after  an  ancestor  removed  by  some  hun- 
dred generations,  but  that  in  each  successive  generation  the 
character  in  question  has  been  lying  latent,  and  at  last,  luidei 
imknown  favorable  conditions,  is  developed.  With  the  barb- 
pigeon,  for  instance,  which  very  rarely  produces  a  blue  bird, 
it  is  probable  that  a  latent  tendency  exists  in  each  generation 
to  produce  blue  plumage.  The  possibility  of  chai'acters  long 
lying  latent  can  be  imderstood  according  to  the  hypothesis  of 
})angenesis,  which  I  have  given  in  another  work.  The  abstract 
improbability  of  a  latent  tendency  being  transmitted  through 
a  vast  number  of  generations,  is  not  greater  tlian  that  of  quite 
useless  or  rudimentary  organs  being  thus  transmitted.  A  mere 
tendency  to  produce  a  nuHment  is  indeed  sometimes  inherited. 
As  all  the  species  of  the  same  genus  are  supposed,  on  our 
theory,  to  be  descended  from  a  connnon  progenitor,  it  might 
be  expected  that  they  would  occasionally  vary  in  an  analogous 
manner;  so  that  the  varieties  of  two  or  more  species  would  re- 
semble each  other,  or  that  a  variety  of  some  one  species  would 
resemble  in  certain  characters  another  and  distinct  species — 
this  other  species  being,  according  to  our  view,  only  a  well- 
marked  and  permanent  variety.  But  characters  thus  gained 
would  probably  be  of  an  unimportant  nature,  for  the  presence 
of  all  important  characters  will  be  governed  by  natural  selec- 
tion, in  accordance  with  tlic  tlifTerent  habits  of  the  species,  and 
Avill  not  be  left  to  the  mutual  action  of  the  nature  of  tlie  organ- 
ism and  of  the  conditions  of  life.  It  might  further  be  expected 
that  the  species  of  the  same  genus  Avould  occasionally  exhil^it 
reversions  to  long-lost  ancestral  characters.  As,  however,  we 
never  know  tlic  exact  character  of  the  common  ancestor  of  a 
natural  group,  we  could  not  distinguish  these  two  cases :  if, 
iV)r  instance,  we  did  not  know  that  the  rock-pigeon  was  not 
feather-footed  or  turn-crowned,  we  could  not  have  told  whether 
these  characters  in  our  domestic  breeds  were  reversions  or  only 
analogous  variations  ;  but  wc  might  have  inferred  that  the  blue 
color  was  a  case  of  reversion  from  llie  number  of  the  markings, 
whicli  arc  correlated  with  this  tint,  and  which  it  docs  not  ap- 


CiiAr.  V.  ANALOGOUS   VAKIATIONS.  Id 

pear  probable  would  all  appear  top^cthcr  from  simple  ^•arialion. 
More  especially  we  might  have  infen-ed  this,  from  the  blue 
color  and  the  several  marks  so  often  appearinp^  when  distinct 
breeds  of  distinct  colors  are  crossed.  Hence,  although  under 
Nature  it  must  generally  be  left  doubtful,  what  cases  are  re- 
versions to  a  formerly-existing  character,  and  what  are  ncAV 
l)ut  analogous  variations,  yet  we  ought,  on  oiu*  theory,  some- 
times to  iind  the  varying  offspring  of  a  species  assuming 
characters  ((^ither  from  nivcrsion  or  from  analogous  variation) 
which  already  are  jirescnt  in  other  members  of  the  same  group 
and  tliis  undoubteclly  is  the  case. 

A  considcrabl(!  jjart  of  the  difficulty  in  recognizing  in  our 
systematic  works  a  variable  species,  is  due  to  its  varieties 
mocking,  as  it  were,  other  species  of  the  same  genus.  A  con- 
siderable catalogue,  also,  could  be  given  of  forms  intermediate 
between  two  other  forms,  which  themselves  can  only  doubt- 
fully be  ranked  as  species ;  and  this  shows,  unless  all  these 
forms  be  considered  as  independently-created  species,  that  the 
one  in  varjing  has  assumed  some  of  the  characters  of  the  other, 
so  as  to  produce  the  intermediate  forms.  But  the  best  evi- 
dence is  afforded  by  parts  or  organs  of  an  important  and  gen- 
erally uniform  nature  occasionally  varying  so  as  to  acquire,  in 
some  degree,  the  character  of  the  same  part  or  organ  in  an 
allied  species.  I  have  collected  a  long  list  of  such  cases ;  but 
here,  as  before,  I  lie  mider  the  great  disadvantage  of  not  being 
able  to  give  them.  I  can  only  repeat  that  such  cases  certainly 
do  occur,  and  seem  to  me  very  remarkable. 

I  will,  however,  give  one  curious  and  complex  case,  not  in- 
deed as  affecting  any  important  character,  but  from  occurring 
in  several  species  of  the  same  genus,  partly  under  domestica- 
tion and  partly  under  Nature.  It  is  a  case  almost  certainly  of 
reversion.  The  ass  sometimes  has  very  distinct  transverse 
bars  on  its  legs,  like  those  on  the  legs  of  the  zebra :  it  has 
been  asserted  that  these  are  jilainest  in  the  foal,  and,  from  in- 
qiiirics  which  I  have  made,  I  believe  this  to  be  true.  The 
stripe  on  the  shoulder  is  sometimes  double  and  is  very  variable 
in  length  and  outline.  A  white  ass,  but  not  an  albino,  has 
been  described  without  either  spinal  or  shoulder  stripe :  and 
these  stripes  are  sometimes  verv  obscure,  or  actually  (luitelost, 
in  dark-colored  asses.  The  koulan  or  Pallas  is  said  to  have 
been  seen  with  a  double  shoulder-stripe.  Mr.  I31yth  has  seen 
a  specimen  of  the  hemionus  with  a  distinct  shoulder-stripe, 
tliough  it  properly  has   none  ;  and  I  have   been   informed  by 


1(32  DISTINCT  SPECIES  PRESENT  Chap.  V. 

Colonel  Poole  tliat  the  foals  of  this  species  arc  generally  striped 
on  the  legs,  and  faiiitly  on  the  shoulder.  The  quagga,  though 
so  plainly  barred  like  a  zebra  over  the  body,  is  without  bars 
on  the  legs ;  but  ]3r.  Gray  has  figured  one  specimen  with  very 
distinct  zebra-like  bars  on  the  hocks. 

"With  respect  to  the  horse,  I  have  collected  cases  in  Eng- 
land of  the  spinal  stripe  in  horses  of  the  most  distinct  breeds, 
and  of  all  colors :  transverse  bars  on  the  legs  are  not  rare  in 
duns,  mouse-duns,  and  in  one  instance  in  a  chestnut:  a  faint 
shoulder-stripe  may  sometimes  be  seen  in  duns,  and  I  have  seen 
a  trace  in  a  bay  horse.  JNIy  son  made  a  careful  examination  and 
sketch  for  me  of  a  dun  Belgian  cart-horse  Avith  a  double  stripe 
on  each  shoulder  and  with  leg-stripes ;  I  have  myself  seen  a 
dun  Devonshire  ponj^,  and  a  small  dun  Welsh  pony  has  been 
carefully  described  to  me,  both  with  three  parallel  stripes  on 
each  shoulder. 

In  the  northwest  part  of  India  the  Kattywar  breed  of  horses 
is  so  generally  striped,  that,  as  I  hear  from  Colonel  Poole,  who 
examined  the  breed  for  the  Indian  Government,  a  horse  with- 
out stripes  is  not  considered  as  purely-bred.  The  spine  is 
always  striped;  the  legs  are  generally  barred;  and  the  shoul- 
der-stripe, which  is  sometimes  double  and  sometimes  treble,  is 
common  ;  the  side  of  the  face,  moreover,  is  sometimes  striped. 
The  stripes  are  often  plainest  in  the  foal ;  and  sometimes  quite 
disappear  in  old  horses.  Colonel  Poole  has  seen  both  gray 
and  bay  Kattywar  horses  striped  Avhen  first  foaled.  I  have 
also  reason  to  suspect,  from  information  given  me  by  Mr.  AV. 
W.  Edwards,  that  Avith  the  English  race-horse  the  spinal  strijie 
is  much  commoner  in  the  foal  than  in  the  full-grown  animal. 
I  have  myself  recently  bred  a  foal  from  a  bay  mare  (offspring 
of  a  Turcoman  horse  and  a  Flemish  mare)  by  a  bay  English 
race-horse  ;  this  foal  when  a  week  old  Avas  marked  on  its  hinder 
quarters  and  on  its  forehead  Avith  numerous,  A'ery  narroAV,  dark, 
zebra-like  bars,  and  its  legs  were  feebly  striped  :  all  the  stripes 
soon  disappeared  completely.  Without  here  entering  on  fur- 
ther details,  I  may  state  that  I  have  collected  cases  of  leg  and 
shoulder  stripes  in  horses  of  A'ery  different  breeds,  in  A'arious 
countries  from  Britain  to  Eastern  China ;  and  from  NorAvay  in 
the  north  to  the  ISIalay  Archipelago  in  the  south.  In  all  jiarts 
of  the  Avorld  these  stripes  occur  far  oftenest  in  duns  and  mouse- 
duns  ;  by  the  term  dun  a  large  range  of  color  is  included,  from 
one  between  broAvn  and  black  to  a  close  approach  to  cream- 
color. 


CnAP.  V.  ANALOGOUS   VAEIATIONS.  163 

I  am  uwaro  tliat  Colonel  Hamilton  Smith,  who  lias  written 
on  this  subject,  believes  that  the  several  breeds  of  the  horse 
are  descended  from  several  abori^^inal  species — one  of  which, 
the  dun,  was  striped ;  and  that  the  above-described  appear- 
ances are  all  due  to  ancient  crosses  with  the  dun  stock.  But 
this  view  may  be  safely  rejected ;  for  it  is  highly  improbable 
that  the  heavy  Belgian  cart-horse,  Welsh  ponies,  cobs,  the  lanky 
Kattywar  race,  etc.,  inhabiting  the  most  distant  parts  of  the 
world,  should  all  have  been  crossed  with  one  supposed  aborigi- 
nal stock. 

Now  let  us  turn  to  the  effects  of  crossing  the  several  species 
of  the  horse-genus.  lloUin  asserts  that  the  common  mule 
from  the  ass  and  horse  is  particularly  apt  to  have  bars  on  its 
legs ;  according  to  Mr.  Gosse,  in  certain  parts  of  the  United 
States  about  nine  out  of  ten  mules  have  striped  legs.  I  once 
saw  a  mule  with  its  legs  so  much  striped  that  any  one  might 
have  thought  that  it  was  a  hybrid-zebra ;  and  Mr.  W.  C.  Mar- 
tin, in  his  excellent  treatise  on  the  horse,  has  given  a  figure  of 
a  similar  mule.  In  four  colored  draAvings,  which  I  have  seen, 
of  hybrids  between  the  ass  and  zebra,  the  legs  were  much  more 
plainly  barred  tlian  the  rest  of  the  body ;  and  in  one  of  them 
there  was  a  double  shoulder-stripe.  In  Lord  Morton's  famous 
hybrid  from  a  chestnut  mare  and  male  quagga,  the  hybrid,  and 
even  the  pure  offspring  subsequently  produced  from  the  mare 
l)y  a  black  Araljian  sire,  were  much  more  plainly  barred  across 
the  legs  than  is  even  the  pure  quagga.  Lastly,  and  this  is  an- 
other most  remarkable  case,  a  hybrid  has  been  figured  by  Dr. 
Gray  (and  he  informs  me  tliat  he  knows  of  a  second  case)  from 
the  ass  and  the  hemionus  ;  and  this  hybrid,  though  the  ass 
only  occasionally  has  stripes  on  his  legs  and  the  hemionus  has 
none  and  has  not  even  a  shoulder-stripe,  nevertheless  had  all 
four  legs  barred,  and  had  throe  short  shoulder-stripes,  like  those 
on  tlie  dun  Devonshire  and  Welsh  ponies,  and  even  had  some 
zebra-like  stripes  on  the  sides  of  its  face.  With  respect  to 
this  last  fact,  I  was  so  convinced  that  not  even  a  stripe  of 
color  appears  from  what  is  commonly  called  chance,  that  I  was 
led  solel}'  from  the  occurrence  of  the  face-stripes  on  this  hybrid 
from  the  ass  and  hemionus  to  ask  Colonel  Poole  whether  such 
face-stripes  ever  occurred  in  the  eminently  striped  Kattywar 
l)reed  of  horses,  and  was,  as  we  have  seen,  answered  in  the 
adirmative. 

AVhat  now  arc  we  to  say  to  these  several  facts  ?  We  sec 
several  very  distinct  species  of  the  horse-genus  becoming,  by 


164  DISTINCT  SPECIES  PRESENT  Cuap.  V, 

siin])le  vaiiiition,  slripod  on  tlio  legs  like  a  zebra,  or  stri})cd  on 
the  sliouUler.s  like  an  ass.  In  the  liorsc  we  see  this  tendency 
strong^  whenever  a  dun  tint  appears — a  tint  Avhidi  approaches 
to  that  of  the  general  coloring'  of  the  other  species  of  the  ge- 
nus. The  appearance  of  the  stripes  is  not  accompanied  by  any 
cliange  of  form  or  by  any  other  new  character.  AVe  see  this 
tendency  to  become  striped  most  strongly  displayed  in  hybrids 
from  between  several  of  the  most  distinct  species.  Now  ob- 
serve the  case  of  the  several  breeds  of  pigeons :  they  are  de- 
scended from  a  pigeon  (including  two  or  three  sub-species  or 
geographical  races)  of  a  bluish  color,  with  certain  bars  and 
other  marlcs  ;  and  Avhcn  any  breed  assmnes  by  simple  variation 
a  l)luish  tint,  these  bars  and  other  marks  invariably  reappear  ; 
but  without  any  other  change  of  form  or  character.  When  the 
oldest  and  truest  breeds  of  various  colors  are  crossed,  wc  sec  a 
strong  tendency  for  the  blue  tint  and  bars  and  marks  to  reap- 
pear in  the  mongrels.  I  have  stated  that  the  most  probable 
hypothesis  to  account  for  the  reappearance  of  xery  ancient 
characters,  is — that  there  is  a  tendency  in  the  young  of  each 
successive  generation  to  produce  the  long-lost  character,  and 
that  this  tendency,  from  unknown  causes,  sometimes  prevails. 
And  we  have  just  seen  that  in  several  species  of  the  horse- 
genus  the  stripes  arc  either  plainer  or  appear  more  commonly 
in  tlie  young  than  in  the  old.  Call  the  breeds  of  pigeons,  some 
of  which  have  bred  true  for  centuries,  species  ;  and  how  exact- 
ly parallel  is  the  case  with  that  of  the  species  of  the  horse- 
genus  !  For  myself,  I  venture  confidently  to  look  back  thou- 
sands on  thousands  of  generations,  and  I  see  an  animal  striped 
like  a  zebra,  but  perhaps  other^vise  very  differently  constructed, 
the  common  parent  of  our  domestic  lu)rse  (whether  or  not  it  be 
descended  from  one  or  more  wild  stocks),  of  the  ass,  the  hemi- 
onus,  quagga,  and  zebra. 

He  who  believes  tliat  each  equine  sjiccies  was  indepen- 
dently created,  will,  I  presume,  assert  that  each  species  has 
been  created  with  a  tendency  t(i  vary,  botli  under  Nature  and 
under  domestication,  in  this  particular  manner,  so  as  often  to 
become  striped  like  other  species  of  tlie  genus ;  and  that  each 
has  been  created  with  a  strong  tendency,  when  crossed  with 
species  inhabiting  distant  quarters  of  tlie  world,  to  produce 
hybrids  resembling  in  tlieir  stri})es,  not  their  own  parents,  but 
other  species  of  the  genus.  To  admit  this  view  is,  as  it  seems 
to  me,  to  reject  a  real  for  an  imreal,  or  at  least  for  an  unknown, 
cause.     It  makes  the  works  of  God  a  mere  mockery  and  decep 


CiiAr.  V.  ANALOGOUS  VARIATIONS.  105 

tioii;  I  would  almost  as  soon  believe  ■with  the  old  and  if^no- 
rant  cosinof>;'oiusts,  that  fossil  shells  had  never  lived,  but  had 
been  created  in  stone  so  as  to  mock  the  shells  living  on  the 
sea-shore. 

Suiiunari/. 

Our  ignorance  of  the  laws  of  variation  is  profound.  Not 
in  one  case  out  of  a  hundred  can  we  pretend  to  assign  any 
reason  why  this  or  that  part  has  varied,  liut  whenever  we 
have  the  means  of  instituting  a  comparison,  the  same  laws 
ajipear  to  have  acted  in  jiroducing  the  lesser  dillerences  be- 
tween varieties  of  the  same  species,  and  the  greater  differences 
between  species  of  the  same  genus.  Changed  conditions  gen- 
erally induce  mere  fluctuating  variability,  but  sometimes  they 
cause  direct  and  definite  effects ;  and  these  may  become 
strpngly  marked  in  the  coiu'se  of  time,  though  we  have  not 
sulhcient  evidence  on  this  head.  Habit  in  producing  constitu- 
tional peculiarities  and  use  in  strengthening  and  disuse  in 
weakening  and  diminishing  organs,  appear  in  many  cases  to 
have  been  potent  in  their  effects.  Homologous  parts  tend  to 
vary  in  the  same  way,  and  homologous  parts  tend  to  cohere, 
ilodilications  in  hard  parts  and  in  external  parts  sometimes 
affect  softer  and  internal  parts.  When  one  part  is  largely 
developed,  perhaps  it  tends  to  draw  nourishment  from  the  ad- 
joining parts ;  and  every  part  of  the  structure  which  can  be 
saved  without  detriment  will  be  saved.  Changes  of  structure 
at  an  early  age  may  aflect  parts  subsefjuently  developed  ;  and 
many  cases  of  correlated  variation,  the  nature  of  which  we  are 
unable  to  understand,  undoubtedly  occur.  Multiple  parts  are 
variable  in  number  and  in  structure,  perhaps  arising  from  such 
])arts  not  having  been  closely  specialized  for  any  particular 
function,  so  that  their  modifications  have  not  been  closely 
checked  by  natural  selection.  It  follows  probably  from  this 
same  cause,  that  organic  beings  low  in  the  scale  are  more  vari- 
able than  those  standing  higher  in  the  scale,  and  which  have 
llieir  whole  organization  more  specialized.  Kudiinentary  or- 
gans, from  being  useless,  are  not  regulated  by  natural  selec- 
tion, and  hence  arc  varial)le.  Specific  characters — that  is,  the 
characters  which  have  come  to  differ  since  the  several  species 
of  (he  same  genus  branched  off  from  a  common  parent — are 
more  varia1)le  than  generics  characters,  or  those  which  have 
long  becii  inherited,  and  have  not  differed  within  this  same 
perioil.     In  these  remarks  we  have  referred  to  special  parts  or 


1G6  SUMMARY.  Chap.  V. 

org-ans  bcin,;^  still  variable,  because  they  have  recently  viiried 
and  thus  come  lo  differ;  but  vrc  have  also  seen  in  the  second 
chapter  that  the  same  principle  applies  to  the  whole  individual ; 
for  in  a  district  Mhcre  many  species  of  any  genus  are  found — 
that  is,  where  there  has  been  much  former  variation  and  differ- 
entiation, or  where  the  manufactory  of  new  specific  forms  has 
been  actively  at  work — in  that  district  and  among  these  spe- 
cies, we  now  find,  on  an  average,  most  varieties.  Secondary 
sexual  characters  are  highly  variable,  and  such  characters  differ 
much  in  the  species  of  the  same  group.  Variability  in  the 
same  parts  of  the  organization  has  generally  been  taken  ad- 
vantage of  in  giving  secondary  sexual  differences  to  the  sexes 
of  the  same  species,  and  specific  differences  to  the  several  spe- 
cies of  the  same  genus.  Any  part  or  organ  developed  to  an 
extraordinary  size  or  in  an  extraordinary  manner,  in  compari- 
son with  the  same  part  or  organ  in  the  allied  species,  must 
have  gone  through  an  extraordinary  amount  of  modification 
since  the  genus  arose ;  and  thus  Ave  can  understand  why  it 
should  often  still  be  variable  in  a  much  higher  degree  than 
other  parts  ;  for  variation  is  a  long-continued  and  slow  process, 
and  natiu"al  selection  will  in  such  cases  not  as  yet  have  had 
time  to  overcome  the  tendency  to  further  variability  and  to 
reversion  to  a  less  modified  state.  But  when  a  species  with 
any  extraordinarily-developed  organ  has  become  the  parent  of 
many  modified  descendants  —  which  on  our  Wew  must  be  a 
very  slow  process,  requiring  a  long  lapse  of  time — in  this  case, 
natural  selection  has  succeeded  in  giving  a  fixed  character  to 
the  organ,  in  however  extraordinary  a  manner  it  may  have 
been  developed.  Species  inheriting  nearly  the  same  constitu- 
tion from  a  common  parent  and  exposed  to  similar  influences, 
natui-ally  tend  to  present  analogous  variations,  or  these  same 
species  may  occasionally  revert  to  some  of  the  characters  of 
their  ancient  progenitors.  Although  new  and  important  modi- 
fications may  not  arise  from  reversion  and  analogous  variation, 
such  modifications  will  add  to  the  beautiful  and  harmonious 
diversity  of  Nature. 

Whatever  the  cause  may  be  of  each  slight  difference  be- 
tween the  offspring  and  their  parents — and  a  cause  for  each 
must  exist — it  is  the  steady  accumulation,  through  natural  se- 
lection, of  beneficial  differences  that  has  given  rise  to  all  those 
modifications  of  structure  which  are  the  most  important  for  the 
welfare  of  each  species. 


Chap.  VI.  DIFFICULTIES  OF  THE  TIIEOKY  1(J7 


CHAPTER  YI. 

DIFFICULTIES    OF   THE   TIIEOKY. 

Difflcnilies  of  the  Theory  of  Descent  with  Modification— Transitions— Ahsence  or 
Karlty  of  Transitional  Varieties— Transitions  in  Habits  of  Life— Diversified  Hab- 
its iu  the  same  Specios— Species  with  Habits  widely  different  from  those  of  their 
Allies — Orj^iiis  of  Extreme  Perfection— Modes  of  Tranh-ition— Cases  of  Ditflcully 
— Natura  nou  fucit  saltnm— Ort'ans  of  small  Importance— Organs  not  in  all  Cases 
absolutely  perfect- The  Law  of  XJniiy  of  Type  aud  of  the  Conditions  of  Existence 
embraced  by  the  Theory  of  Natural  Selection. 

Loxr,  before  havins;  anivcd  at  this  part  of  my  ^-ork,  a 
crowd  of  dilFiculties  will  have  occurred  to  the  reader.  Some 
of  them  are  so  serious  that  to  this  day  I  can  hardly  reflect  on 
them  without  bein<i;  stapffrered ;  but,  to  the  best  of  my  judf^- 
ment,  the  prreater  number  arc  only  «pparcnt,  and  those  that  are 
real  are  not,  I  think,  fatal  to  my  theory. 

These  dilliculties  and  objections  may  be  classed  under  the 
followiuf^  heads :  First,  Avhy,  if  species  have  descended  from 
other  species  by  insensibly  line  p;radations,  do  Ave  not  every- 
where see  ir.numcrable  transitional  fonns?  Why  is  not  all 
nature  in  confusion,  instead  of  the  species  being,  as  we  see 
them,  well  defined  ? 

Secondly,  is  it  possible  that  an  animal  liavino",  for  instance, 
the  structure  and  habits  of  a  bat,  could  have  been  formed  by 
the  modification  of  some  animal  Avith  Avidely-difl'erent  structine 
and  habits  ?  Can  Ave  believe  that  natural  selection  could  pro- 
duce, on  the  one  hand,  organs  of  trifling  importance,  such  as 
the  tail  of  a  giraffe,  Avhich  serA'cs  as  a  tly-fiapper,  and,  on  the 
other  hand,  organs  of  sucli  wonderful  structure,  as  the  eye,  of 
Avhich  we  hardly  as  yet  fiillv  imderstand  the  inimitable  perfec- 
tion ? 

Thirdly,  can  instincts  be  acquired  and  modified  through 
natural  selection  ?  What  shall  Ave  say  to  so  marvellous  an 
instinct  as  that  Avhich  leads  the  bee  to  make  cells,  Avhich  has 
jiracticall}^  anticipated  i\m  discoveries  of  profound  mathema- 
ticians ? 


108  ABSENCE  OR  EAEITY  Cii-vp.  VI. 

Fourthl}',  how  can  -wc  account  for  species,  Vv'hen  crossed, 
being  sterile  and  jiroducins;^  sterile  offsprinp-,  "vvhcreas,  when 
varieties  are  crossed,  their  fertility  is  unimpaired? 

Tiie  tlrst  two  heads  shall  be  here  discussed — Instinct  and 
Hybridism  in  separate  chapters. 

On  the  Absence  or  Harlty  of  Transltio7ial  Varieties. 

As  natural  selection  acts  solely  by  the  preservation  of 
profitable  modifications,  each  new  form  will  tend  in  a  fully- 
stocked  country  to  take  the  place  of,  and  finally  to  exterminate, 
its  own  less  improved  parent-form  and  other  less-favored  forms 
with  Avhich  it  comes  into  competition.  Thus  extinction  and 
natural  selection  go  hand  in  hand.  Hence,  if  we  look  at  each 
species  as  descended  from  some  other  iniknown  form,  both  the 
parent  and  all  the  transitional  varieties  will  generally  have 
been  exterminated  by  the  very  process  of  the  formation  and 
perfection  of  the  new  form. 

But,  as  by  this  theory  innumerable  transitional  forms  must 
have  existed,  why  do  we  not  find  them  embedded  in  countless 
numbers  in  the  crust  of  the  earth.  It  will  be  more  convenient 
to  discuss  tliis  question  in  the  chapter  on  the  Imperfection  of 
the  Geological  liccord ;  and  I  will  here  only  st:ite  that  I  be- 
lieve the  answer  mainly  lies  in  the  record  being  incomparably 
less  perfect  than  is  generally  supposed.  The  crust  of  the  earth 
is  a  vast  museum  ;  but  the  natural  collections  have  been  imper- 
fectly made,  and  only  at  long  intervals  of  time. 

But  it  may  be  lu-ged  that  when  several  closely-allied  species 
inhabit  the  same  teixitory,  we  surely  ought  to  find  at  the  pres- 
ent time  many  transitional  forms.  Let  us  take  a  simple  case : 
in  travelling  from  north  to  south  over  a  continent,  we  generally 
meet  at  successive  intervals  with  closely-allied  or  representa- 
tive species,  (Tvidently  tilling  neaily  the  same  place  in  the  nat- 
ural economy  of  the  land.  These  reiM-esentativc  species  often 
meet  and  interlock ;  and  as  the  one  l)ecomcs  rarer  and  rarer, 
the  other  becomes  more  and  more  fret(uent,  till  the  one  re- 
places the  other.  But  if  we  compare  these  species  Avhere  they 
intermingle,  they  are  generally  as  absolutel}"  distinct  from  each 
other  in  every  detail  of  structiu'c  as  are  specimens  taken  from 
the  metropolis  inhalntcd  by  each.  By  my  tlieory  these  allied 
species  are  descended  from  a  common  parent ;  and,  during  the 
jHoccss  of  modilication,  each  has  become  adapted  to  the  con- 
ditions of  lift^  of  its  own  region,  and  has  suj^planted  and  ex- 


CiiAr.  VI.  OF  TRANSITIONAL  VAKIETIES.  169 

IcriniiKited  its  ori^i'inal  parent-form  and  all  the  transitional  va- 
rieties between  its  past  and  present  states.  Hence  we  ought 
not  to  expect  at  the  present  time  to  mccft  with  numerous  tran- 
sitional varieties  in  each  rei^ion,  though  they  must  have  ex- 
isted there,  and  may  be  embedded  there  in  a  fossil  condition. 
But  in  the  intermediate  region,  having  intermediate  conditions 
of  life,  why  do  we  not  now  find  closely-linking  intermediatt^ 
varieties?  This  dilliculty  for  a  long  time  quite  confounded 
nie.     But  I  think  it  can  be  in  large  part  explained. 

In  the  lii-st  jjlace,  we  should  be  extremely  cautious  in  infer- 
ring, be(\iuse  an  area  is  now  continuous,  that  it  has  been  con- 
tinuous during  a  long  period.  Geology  would  lead  us  to  be- 
lieve that  most  continents  have  been  broken  up  into  islands 
even  during  the  later  tertiary  periods ;  and  in  such  islands 
distinct  species  might  have  been  separately  formed  without 
the  possibilit}'  of  intermediate  varieties  existing  in  the  inter- 
mediate zones.  By  changes  in  the  form  of  the  land  and  of 
climate,  marine  areas  now  continuous  must  often  have  existed 
within  recent  times  in  a  far  less  continuous  and  uniform  condi- 
tion than  at  present.  But  I  will  pass  over  this  way  of  escaj> 
ing  from  the  difficulty ;  for  I  believe  that  many  perfcctlj^Ie- 
fmed  sjiecies  have  been  formed  on  strictly  continuous  areas ; 
though  I  do  not  doubt  that  the  formerly  broken  condition  of 
areas  now  continuous  has  played  an  important  part  in  the  for- 
mation of  new  species,  more  especially  ^vith  frcelj'-crossing  and 
wandering  animals. 

In  looking  at  species  as  they  are  now  distributed  over  a 
^vide  area,  we  generally  find  them  tolerably  numerous  over  a 
large  territory,  then  becoming  somewhat  abruptly  rarer  and 
rarer  on  the  confines,  and  finally  disappearing.  Hence  the 
neutral  territory  between  two  representative  species  is  gener- 
ally narrow  in  comparison  with  the  territory  projier  to  each. 
^^'e  see  the  same  fact  in  ascending  mountains,  and  sometimes 
it  is  quite  remarkable  how  abruptly,  as  Alph.  de  Candollc  has 
(il)served,  a  common  alpine  species  disappears.  The  same  fact 
has  been  noticed  by  E.  Forbes  in  sounding  the  depths  of  the 
s(>a  with  the  dredge.  To  those  who  look  at  climate  and  the 
])]iysical  conditions  of  life  as  the  all-important  elements  of  dis- 
tribution, these  facts  ought  to  cause  surprise,  as  climate  and 
height  or  depth  graduate  away  insensibly.  But  when  we  bear 
in  mind  that  almost  every  species,  even  in  its  metropolis,  would 
increase  immensely  in  numbeis,  were  it  not  for  other  com- 
peting species;  that  nearly  aH  either  prey  on  or  serve  as  prey 
s 


170  ABSENCE  OF  RARITY  Chap.  VI. 

for  otlicrs ;  in  short,  that  cadi  organic  beinf^  is  cither  directly 
or  indirectly  related  in  the  most  important  manner  to  other 
organic  beings,  \vc  must  see  that  the  range  of  the  inhabitants 
of  any  country  by  no  means  exclusively  depends  on  insensibly 
changing  pliysical  conditions,  but  in  large  part  on  the  presence 
of  other  species,  on  which  it  lives,  or  by  ■which  it  is  destroyed, 
or  with  which  it  comes  into  comjietition ;  and  as  these  species 
arc  already  defmed  objects,  not  blending  one  into  another  by 
insensil)le  gradations,  the  range  of  any  one  species,  depending 
as  it  does  on  the  range  of  others,  will  tend  to  be  sharply  de- 
fined. Moreover,  each  species  on  the  confines  of  its  range, 
wherc  it  exists  in  lessened  numbers,  will,  during  fluctuations 
in  the  number  of  its  enemies  or  of  its  prey,  or  in  the  seasons, 
be  extremely  liable  to  utter  extermination  ;  and  thus  its  geo- 
graphical range  Avill  come  to  be  still  more  sharply  defined. 

If  I  am  right  in  believing  that  allied  or  representative  spe- 
cies, when  inhabiting  a  continuous  area,  are  generally  so  dis- 
tributed that  each  has  a  wide  range,  with  a  comparatively 
narrow  neutral  territory  between  tliem,  in  which  they  become 
rather  suddenly  rarer  and  rarer ;  then,  as  varieties  do  not  essen- 
tially differ  from  species,  the  same  rule  will  probably  apply  to 
both ;  and  if  we  take  a  varying  species  inhabiting  a  very  large 
area,  we  shall  have  to  adapt  two  varieties  to  two  large  areas, 
and  a  third  variety  to  a  narrow  intermediate  zone.  The  inter- 
mediate variety,  consequently,  will  exist  in  lesser  numbers 
from  inhabiting  a  narrow  and  lesser  area ;  and  practical!}',  as 
fiir  as  I  can  make  out,  this  rule  holds  good  with  varieties  in  a 
state  of  Tjature.  I  have  met  with  striking  instances  of  the 
rule  in  the  case  of  varieties  intermediate  between  well-marked 
varieties  in  the  genus  Balanus.  And  it  would  appear  from 
information  given  me  by  ]\Ir.  "Watson,  Dr.  Asa  Gray,  and  Mr. 
Wollaston,  that  generally,  when  varieties  intermediate  between 
two  other  forms  occur,  they  arc  much  rarer  numerically  than 
the  forms  which  they  connect.  Now,  if  we  may  trust  these 
facts  and  inferences,  and  therefore  conclude  that  varieties  link- 
ing two  other  varieties  together  hare  generally  existed  in 
lesser  numbers  than  the  forms  which  they  connect,  then,  I  think, 
we  can  understand  wh}'  intermediate  varieties  should  not  en- 
dure for  very  long  periods  ;  Avhy,  as  a  general  rule,  they  should 
be  exterminated  and  disaiii)ear,  sooner  than  the  forms  v>hich 
they  originally  linked  together. 

"For  any  form  existing  in  lesser  numbers  would,  as  already 
remarked,  ran  a  greater  chance  of  being  exterminated  tlian 


CuAi-.  VI.  OF  TRANSITIOXAL  VARIETIES.  171 

one  exist inn"  in  laro-c  numbers;  and  in  this  particular  case  the 
interniedi:it(!  form  would  be  cminentl}"^  liable  to  the  inroads 
of  closely-allied  forms  existing  on  both  sides  of  it.  But  a  far 
more  important  consideration,  as  I  believe,  is  that,  during  the 
process  of  further  modification,  by  Avhich  two  varieties  are 
supposed  to  be  converted  and  perfected  into  two  distinct  spe- 
cies, the  two  which  exist  in  larger  numbers,  from  inhabiting 
larger  areas,  will  have  a  great  advantage  over  the  intermediate 
variet}',  which  exists  in  smaller  numbers  in  a  narrow  and  inter- 
mediate zone.  For  forms  existing  in  larger  numbers  will  al- 
ways have  a  better  chance,  within  any  given  period,  of  present- 
ing further  favorable  variations  for  natural  selection  to  seize 
on,  than  will  the  rarer  fcjrms  which  exist  in  lesser  numbers. 
Hence,  the  more  common  forms,  in  the  race  for  life,  will  tend 
to  beat  and  supplant  the  less  common  forms,  for  these  will  be 
more  slowly  modified  and  improved.  It  is  the  same  principle 
which,  as  I  believe,  accounts  for  the  common  species  in  each 
country,  as  shown  in  the  second  chapter,  presenting  on  an 
average  a  greater  number  of  well-marked  varieties  than  do  the 
rarer  species.  I  may  illustrate  what  I  mean  by  supposing  three 
varieties  of  sheep  to  be  kept:  one  adapted  to  an  extensive 
mountainous  region  ;  a  second  to  a  comparatively  narrow,  hilly 
tract ;  and  a  third  to  wide  plains  at  the  base ;  and  that  the 
inhabitants  are  all  trying  with  equal  steadiness  and  skill  to 
improve  their  stocks  by  selection ;  the  chances  in  this  case  will 
be  strongly  in  favor  of  the  great  holders  on  the  mountains  or 
on  the  plains  improving  th.eir  breeds  more  quicldy  than  the 
small  holders  on  the  intermediate  narrow,  hilly  tract;  and  con- 
sequently the  improved  mountain  or  j^lain  breed  Avill  soon 
take  the  place  of  the  less  improved  hill-breed ;  and  thus  the 
two  breeds,  which  originally  existed  in  greater  numbers,  will 
come  into  close  contact  with  each  other,  without  the  interpo- 
sition of  the  supplanted,  intermediate  hill-variety. 

To  sum  up,  I  believe  that  species  come  to  be  tolerabh'  well- 
dcfini^d  objects,  and  do  not  at  any  one  period  present  an  inex- 
tricable chaos  of  varying  and  intermediate  links  :  first,  because 
new  varieties  are  very  slowly  formed,  for  variation  is  a  slow 
])roccss,  and  natural  selection  can  do  nothing  until  favorable 
individual  diflerences  or  variations  occur,  and  until  a  place  in 
the  natural  polity  of  the  country  can  be  better  filled  by  some 
modification  of  some  one  or  more  of  its  inhabitants.  And  such 
«ncw  places  will  depend  on  slow  changer>  of  climate,  or  on  the 
occasional  innnigratinn  of  new  inhabitants,  and,  ]m)bably,  in  a 


172  ABSENCE  OR  IJARITY  Chap.  VI. 

still  more  important  doffrco,  on  some  of  the  old  inhabitants  be- 
coming slowly  moditied,  with  the  new  forms  thus  produced 
and  the  old  ones  acting  and  reacting  on  each  other.  So  that, 
in  any  one  region  and  at  any  one  time,  we  ought  only  to  sec 
a  few  species  j)resenting  slight  modiiications  of  structure  in 
some  degree  permanent ;  and  this  assuredly  we  do  see. 

Secondly,  areas  now  continuous  must  often  have  existed 
within  the  recent  period  as  isolated  portions,  in  which  many 
forms,  more  especially  among  the  classes  which  unite  for  each 
birth  and  wander  much,  may  have  separately  been  rendered 
suiKciently  distinct  to  rank  as  representative  species.  In  this 
case,  intermediate  varieties  betw^een  the  several  representative 
species  and  their  common  parent,  must  have  existed  formerly 
within  each  isolated  portion  of  the  land,  but  these  links  during 
the  process  of  natural  selection  will  have  been  supplanted  and 
exterminated,  so  that  they  will  no  longer  be  found  in  a  living 
state. 

Thirdly,  wlien  two  or  more  varieties  have  been  formed  in 
diflerent  j)ortions  of  a  strictly  continuous  area,  intermediate 
varieties  Avill,  it  is  probable,  at  first  have  been  formed  in  the 
intermediate  zones,  but  they  Avill  generally  have  had  a  short 
duration.  For  these  intermediate  varieties  will,  from  reasons 
already  assigned  (namely,  from  what  we  know  of  the  actual 
distribution  of  closely-allied  or  representative  species,  and  like- 
Avise  of  acknowledged  varieties),  exist  in  the  intermediate  zones 
in  lesser  numbers  than  the  varieties  which  they  tend  to  con- 
nect. From  this  cause  alone  the  intennediate  varieties  will 
be  hable  to  accidental  extemiination  ;  and  during  the  process 
of  further  modification  through  natural  selection,  they  will  al- 
most certainly  lie  beaten  and  supplanted  by  the  forms  which 
they  connect ;  for  these  from  existing  in  greater  numbers  will, 
in  the  aggregate,  present  more  variation,  and  thus  be  further 
improved  through  natural  selection  and  gain  further  advan- 
tages. 

Lastly,  looking  not  to  any  one  time,  but  to  all  time,  if 
my  theory  be  true,  numberless  intermediate  varieties,  linking 
closely  together  all  the  species  of  the  same  grouji,  must  assur- 
edly have  existed;  but  the  very  process  of  natural  si'leetion 
constantly  tends,  as  has  been  so  often  remarked,  to  exterminate 
the  parent-forms  and  the  intermediate  links.  Consequently 
evidence  of  their  former  existence  could  be  found  only  among 
fossil  remains,  Avhich  are  preserved,  as  we  shall  in  a  future* 
chapter  attempt  to  show,  in  an  extremely  imperfect  and  inter- 
mittent record. 


CiiAi-.  VI,  OF  TRANSITIONAL  VARIETIES.  173 

On  the  Origin  and  IW'nsifions  of  Orr/anlc  Heings  wifhjjecH' 
liar  Habits  and  /Structure. 

It  has  been  asked  by  the  opponents  of  such  views  as  I  hold, 
how,  for  instance,  a  land  carnivorous  animal  could  have  been 
converted  into  one  with  aquatic  habits  ;  for  how  could  tlu;  ani- 
mal in  its  transitional  state  have  subsisted  ?  It  would  be  easy 
to  show  that  within  the  same  group  carnivorous  animals  exist, 
having'  every  intermediate  grade  between  truly  aquatic  and 
strictly  terrestrial  habits  ;  and  as  each  exists  by  a  struggle  for 
life,  it  is  clear  that  each  is  well  adapted  in  its  habits  to  its 
place  in  Nature.  Look  at  the  Mustela  vison  of  North  Amei-ica, 
which  has  webbed  feet,  and  which  resembles  an  otter  in  its  fur, 
short  legs,  and  form  of  tail;  during  summer  this  animal  dives 
for  and  preys  on  fish,  but  during  the  long  winter  it  leaves  the 
frpzen  waters,  and  iM'e3'S,  like  other  polecats,  on  mice  and  land 
animals.  If  a  different  case  had  been  taken,  and  it  had  1)een 
asked  how  an  insectivorous  quadruped  could  possibly  have 
been  converted  into  a  flying  bat,  the  question  would  have  been 
far  more  difficult  to  answer.  Yet  I  think  such  difficulties  have 
little  weight. 

Here,  as  on  other  occasions,  I  lie  imder  a  heavy  disadvan- 
tage, for,  out  of  the  many  striking  cases  which  I  have  collected, 
I  can  give  only  one  or  two  instances  of  transitional  hal)its  and 
structures  in  closely-allied  species  of  the  same  genus;  and  of 
diversified  habits,  either  constant  or  occasional,  in  the  satiKj 
species.  And  it  seems  to  me  that  nothing  less  than  a  long 
list  of  such  cases  is  sufficient  to  lessen  the  difficulty  in  an}-  ])ar- 
ticidar  case  like  that  of  the  bat. 

Ix)ok  at  the  family  of  squirrels  :  here  we  have  the  finest  gra- 
dation from  animals  with  their  tails  only  slightly  flattened,  and 
from  others,  as  Hir  J.  IJichardson  has  remarked,  with  the  pos- 
terior part  of  their  bodies  rather  wide  and  with  the  skin  on 
their  flanks  rather  full,  to  the  so-called  flying-squirrels  ;  and  fly- 
ing-squirrels have  their  limbs  and  even  the  base  of  the  tail  united 
l)y  a  broad  expanse  of  skin,  which  serves  as  a  parachute  and 
allows  them  to  glide  through  the  air  to  an  astonishing  distance 
from  tree  to  tree.  We  cannot  doubt  that  each  structure  is  of 
use  to  each  kind  of  squirrel  in  its  own  country,  by  enabling  it 
to  escape  birds  or  beasts  of  prey,  or  to  coUect  food  moie 
quickly,  or,  as  there  is  reason  to  believe,  by  lessming  the  dan- 
ger from  occasional  falls,  lint  it  does  not  follow  from  this  fact 
that  the  structure  of  each  sfjuirrel  is  the  best  that  it  is  possible 


l^.t  TKANSITIOXS  Chat.  VI. 

lo  conceive  under  all  natural  conditions.  Lot  the  climate  and 
vegetation  change,  let  other  coTnpcting  rodents  or  new  beasts 
of  prey  immigrate,  or  old  ones  become  modified,  and  all  anal- 
ogy would  lead  us  to  believe  that  some  at  least  of  the  squirrels 
would  decrease  in  numbers  or  become  exterminated,  unless 
they  also  became  modified  and  improved  in  structure  in  a  cor- 
responding manner.  Therefore,  I  can  see  no  difficulty,  more 
especially  under  changing  conditions  of  life,  in  the  continued 
preservation  of  individuals  with  fuller  and  fuller  flunk-mem- 
branes, each  modification  being  useful,  each  being  propagated, 
until,  by  the  accumulated  efl'ects  of  this  process  of  natural  selec- 
tion, a  perfect  so-called  flying-squirrel  was  produced. 

Now  look  at  the  Galeopithecus,  or  flying  lemur,  which  for- 
merly was  ranked  among  bats.  It  has  an  extremely  wide 
flank-membrane,  stretching  from  the  corners  of  the  jaw  to  the 
tail,  and  including  the  limbs  and  the  elongated  fingers  :  the 
flank-membrane  is,  also,  furnished  with  an  extensor  muscle. 
Although  no  graduated  links  of  stracture,  fitted  for  gliding 
through  the  air,  now  connect  the  Galeopithecus  with  the  other 
LemuridcTJ,  yet  there  is  no  difficulty  in  supposing  that  such  links 
formerly  existed,  and  that  each  had  been  formed  by  the  same 
steps  as  in  the  case  of  the  less  perfectly  gliding  squurels  ;  and 
that  each  grade  of  structure  was  useful  to  its  possessor.  Nor 
can  I  see  any  insuperable  difficulty  in  further  belie\-ing  it  possi- 
ble that  the  membrane-connected  fingers  .and  forearm  of  the 
Galeopithecus  might  be  greatly  lengthened  by  natural  selec- 
tion ;  and  this,  as  far  as  the  organs  of  flight  'are  concerned, 
would  convert  it  into  a  bat.  In  certain  bats  which  have  the 
wing-mem])rane  extended  from  the  top  of  the  shoulder  to  the 
tail,  including  the  hind  legs,  we  perhaps  yet  see  actual  traces 
of  an  apparatus  originally  fitted  for  gliding  through  the  air 
rather  than  for  flight. 

If  about  a  dozen  genera  of  birds  had  become  extinct  or 
were  unknown,  who  would  have  ventured  to  surmise  that  birds 
might  have  existed  which  used  their  wings  solely  as  flappers, 
like  the  logger-headed  duck  (Micropterus  of  Eyton) ;  as  tins  in 
the  water  and  front  legs  on  the  land,  like  the  penguin;  as 
sails,  like  the  ostrich  ;  and  functionallj'  for  no  purpose,  like  the 
Apteryx?  Yet  the  structure  of  each  of  these  birds  is  good  for 
it,  under  the  conditions  of  life  to  which  it  is  exposed,  for  each 
has  to  live  by  a  struggle ;  but  it  is  not  necessarily  the  best 
possible  under  all  possible  conditions.  It  must  not  be  inferred 
from  these  remarks  tliat  any  of  the  grades  of  wing-structure 


Chap.  VI.  OF  ORGANIC  BEINGS.  175 

here  alluded  to,  ■\vliicli  j)c*rliiips  may  all  have  resulted  from  dis- 
use, indicate  the  natural  stops  by  whicli  birds  have  acquired 
their  perfect  jK)wer  of  ilifj^ht ;  but  they  serve,  at  least,  to  show 
what  diversified  means  of  transition  are  possible. 

Seeing  that  a  few  members  of  such  water-breathing  classes 
as  tlie  Crustacea  and  Mollusca  are  adapted  to  live  on  the  land; 
and  seeing  that  we  have  flying  birds  and  mammals,  lining  in- 
sects of  the  most  divei-sified  types,  and  formerly  had  Hying  rej)- 
tiles,  it  is  conceivable  that  liying-flsh,  Mhich  now  glide  far 
through  the  air,  slightly  rising  and  turning  by  the  aid  of  their 
fluttering  llns,  might  liave  been  modified  into  perfectly-winged 
animals.  K  this  had  Ix^en  effected,  who  would  have  ever  im- 
agined that  in  an  early  ti-ansitional  state  they  had  been  the  in- 
habitants of  the  open  ocean,  and  had  used  their  incipientorgans 
of  flight  exclusively,  as  far  as  wc  know,  to  escape  being  de- 
voured by  other  fish  ? 

AVhen  m'C  see  any  structure  liighlj'  perfected  for  an}-  par- 
ticular habit,  as  the  wings  of  a  bird  for  llight,  we  should  bear 
in  mind  that  animals  displaying  early  transitional  grades  of  the 
structure  will  seldom  exist  at  the  present  day,  lor  they  will 
have  been  supplanted  by  their  successors,  which  Avere  gradu- 
ally rendered  more  perfect  through  natural  selection.  Further- 
more, we  may  conclude  that  transitional  states  between  struct- 
ures fitted  for  very  difl'erent  habits  of  life  Avilkrarely  have  been 
developed  at  an  early  period  in  great  numbers  and  under  many 
subordinate  forms.  Thus,  to  return  to  our  imaginary  illustra- 
tion of  the  llying-fish,  it  does  not  seem  probable  that  fishes 
capable  of  true  flight  would  have  been  develoi^ed  under  many 
subordinate  forms,  for  taking  prey  of  many  kinds  in  many 
ways,  on  the  land  and  in  the  water,  imtil  their  organs  of  flight 
had  come  to  a  high  stage  of  perfection,  so  as  to  have  given 
them  a  decided  advantage  over  other  animals  in  the  battle  for 
life.  Hence  the  chance  of  discovering  species  with  transition- 
al grades  of  structure  in  a  fossil  condition  will  always  be  less, 
from  their  having  existed  in  lesser  numbers,  than  in  the  case 
of  species  with  fully-developed  structures. 

I  will  now  give  two  or  three  ihstances  of  diversified  and  of 
changed  habits  in  the  individuals  of  the  same  species.  In 
either  case  it  Avould  be  easy  for  natural  selection  to  adapt  the 
structure  of  the  animal  to  its  changed  habits,  or  exclusively  to 
one  of  its  several  habits.  It  is,  however,  dilhcult  to  decide,  and 
immaterial  for  us,  whether  habits  generally  change  first  and 
structure  afterward  ;  or  Avhether  slight  modifications  of  struo 


17G  TRANSITIONS  Chap.  VI. 

turc  lead  to  clian^ed  habits ;  botli  probably  often  occurring-  al- 
most sinuiltaneouslj.  Of  cases  of  champed  habits  it  will  sullice 
merely  to  allude  to  that  of  the  many  British  insects  which  now- 
feed  on  exotic  plants,  or  exclusively  on  artificial  substances. 
Of  diversified  habits  innumerable  instances  could  Ixi  given  :  I 
have  often  watched  a  tyrant  flycatcher  (Sauropha<^us  sulphu- 
ratus)  in  South  America,  hovering  over  one  spot  and  then 
proceeding  to  another,  like  a  kestrel,  and  at  other  times  stand- 
ing stationary  on  the  margin  of  water,  and  then  dashing  into 
it  like  a  kingfisher  at  a  fish.  In  our  own  country  the  larger 
titmouse  (Parus  major)  may  be  seen  climbing  branches,  almost 
like  a  creeper ;  it  sometimes,  like  a  shrike,  kills  small  birds  by 
blows  on  the  head  ;  and  I  have  many  times  seen  and  heard  it 
hammering  the  seeds  of  the  yew  on  a  branch,  and  thus  break- 
ing them  like  a  nuthatch.  In  North  xVmerica  the  black  bear 
was  seen  by  Hearne  swimming  for  hours  with  widely-open 
mouth,  thus  catching,  almost  like  a  whale,  insects  in  the  water. 
As  we  sometimes  see  individuals  of  a  species  following 
habits  widely  different  from  those  of  their  own  species  and  of 
the  other  species  of  the  same  genus,  "we  might  expect  that 
such  individuals  Avould  occasionally  give  rise  to  new  sjiccies, 
having  anomalous  habits,  and  with  their  structure  either 
slightly  or  considerably  modified  from  that  of  their  proper 
type.  And  such*nstanc<?s  do  occur  in  Nature.  Can  a  more 
striking  instance  of  adaptation  be  given  than  that  of  a  wood- 
pecker for  climbing  trees  and  seizing  insects  in  the  chinks  of  the 
bark  ?  Yet  in  North  America  there  are  Avoodpcckci-s  which 
feed  largely  on  fruit,  and  others  with  elongated  wings  which 
chase  insects  on  the  wing.  On  the  plains  of  La  Plata,  where 
not  a  tree  grows,  there  is  a  woodpecker  (Colaptcs  campestris) 
which  has  two  toes  before  and  two  behind,  a  long  pointed 
tongue,  pointed  tail-feathers,  sufficiently  stiff  to  support  the 
bird  in  a  vertical  position  on  a  post,  but  not  so  stiff  as  in  the 
typical  woodpeckers,  and  a  straight,  strong  beak.  The  beak, 
however,  is  not  so  straight  or  so  strong  as  in  the  typical  wood- 
peckers, but  it  is  strong  enough  to  bore  into  wood.  Hence  this 
Colaptes  in  all  the  essential  parts  of  its  structure  is  a  Avoodptxk- 
er.  Even  in  such  trifling  characters  as  the  coloring,  the  harsh 
tone  of  the  voice,  and  inidulatory  flight,  all  plainly  dcclareil  its 
close  blood-relationship  to  ouj  common  Avoodpecker  ;  yet,  as  I 
can  assert,  not  only  from  my  own  observation,  but  from  that 
of  the  accurate  Azara,  it  never  climbs  a  tree  !  I  may  mention, 
as  another  illustration  of  the  varied  haliits  of  the  tril)C,  that  a 


f^^ 


CiiAP.  VI.  OF  ORGANIC  BEINGS.  177 

Mexican  Colaptes  has  been  described  by  Do  Saussurc  as  boring 
holes  into  hard  wood  in  order  to  hiy  up  a  store  of  acorns,  but 
for  what  use  is  not  yet  known. 

Petrels  are  the  most  ar-rial  and  oceanic  of  l)inls,  l)ut  in  the 
quiet  sounds  of  Tierra  del  Fucf^o,  the  Pulhnuria  berardi,  in  its 
l^eneral  habits,  in  its  astouisliinii^  power  of  divinjr,  its  manner 
of  swiinminij;-,  and  of  flying  when  made  to  take  lliglit,  would  be 
mistaken  by  anyone  for  an  auk  or  a  grebe;  nevertheless  it  is  es- 
sentially a  petrel,  but  with  many  parts  of  its  organization  pro- 
foundly modified  in  relation  to  its  new  haliits  of  life ;  Avhereas 
the  woodpecker  of  L:i  Plata  has  had  its  structure  only  slightly 
modified.  In  the  case  of  the  Avater-ouzcl,  the  acutest  observer 
by  examining  its  dead  body  would  never  have  suspected  its 
sub-aquatic  hal)its;  yet  this  binl,  which  is  allied  to  the  thrusli 
familv,  wholly  subsists  by  diving  —  using  its  wings  under 
\yater,  and  grasjiing  stones  with  its  feet.  AH  the  members  of 
the  great  order  of  Hymenopterous  insects  are  terrestrial,  ex- 
cepting the  genus  Proctotrupes,  which  Sir  J(jhn  Lubbock  has 
recently  discovered  to  be  aquatic  in  its  habits  ;  it  often  enters 
the  water  and  dives  about  by  the  use  not  of  its  legs  but  of  its 
wings,  and  remains  as  long  as  four  hours  beneath  the  surface  ; 
yet  not  the  least  modification  in  its  structure  can  be  detected 
in  accordance  Anth  such  abnormal  habits. 

He  who  believes  that  eacli  being  has  been  created  as  we 
now  see  it,  must  occasionally  have  felt  surprise  when  he  has 
met  with  an  animal  having  habits  and  structure  not  at  all  in 
agreement.  What  can  be  jilaincr  than  that  the  webbed  feet  of 
ducks  and  geese  are  formed  for  swimming  ?  Yet,  there  are  up- 
land geese  with  webbed  feet  which  rarely  or  never  go  near  the 
water;  and  no  one  except  Audubon  has  seen  the  frigate-bird, 
which  has  all  its  four  toes  webbed,  alight  on  the  surface  of  the 
ocean.  On  the  other  hand,  grebes  and  coots  are  eminently 
aquatic,  although  their  toes  are  only  bordered  by  membrane. 
What  .seems  jilaincr  than  that  the  long  toes,  not  furnished  with 
membrane,  of  the  Grallatores  are  formed  for  walking  over 
swamps  and  lloating  plants?  The  water-hen  and  landrail  are 
members  of  this  order,  yet  the  first  is  nearly  as  acjuatic  as  the 
coot,  and  the  second  nearly  as  terrestrial  as  the  quail  or  ])ar- 
tridge.  In  such  eases,  and  many  others  could  be  given,  habits 
have  changc^d  Avithout  a  corresponding  change  of  structure. 
The  webbed  feet  of  the  upland  goose  may  be  said  to  have  be- 
come rudimentary  in  function,  though  not  in  structure.     In  the 


178  ORGANS   OF   EXTREME  PERFECTION  Chap.  VI. 

frigate-bird,  the  dee])ly-scooped  membrane  between  the  toes 
shows  that  structure  has  begun  to  change. 

He  Avho  believes  in  separate  and  innumerable  acts  of  crea- 
tion may  say,  that  in  these  cases  it  has  pleased  the  Creator  to 
cause  a  being  of  one  type  to  take  the  place  of  one  belonging  to 
another  t^-pe ;  but  this  seems  to  me  only  restating  the  fact  in 
ditrnified  lano-uaffe.  He  Avho  believes  in  the  strug"-le  for  ex- 
istcnce  and  in  the  principle  of  natural  selection,  will  acknowl- 
edge that  every  organic  being  is  constantly  endeavoring  to 
increase  in  numbers  ;  and  that  if  any  one  varies  ever  so  little, 
either  in  habits  or  structure,  and  thus  gains  an  advantage  over 
some  other  inhabitant  of  the  country,  it  will  seize  on  the  j)lace 
of  that  inhabitant,  however  different  it  may  be  from  its  own 
place.  Hence  it  will  cause  him  no  surprise  that  there  should 
be  geese  and  frigate-birds  with  webbed  feet,  living  on  the  dry 
land,  or  most  rai'ely  alighting  on  the  "water;  that  there  should 
be  long-toed  corncrakes,  living  in  meadows  instead  of  in 
swamps ;  that  there  should  be  woodpeckers  Mhere  not  a  tree 
grows  ;  that  there  should  be  diving  thnishes  and  diving  Hymen- 
optera,  and  petrels  with  the  habits  of  auks. 

Organs  of  Extreme  Perfection  and  Complication. 

To  suppose  that  the  eye  with  all  its  inimitable  contrivances 
for  adjusting  the  focus  to  different  distances,  for  admittmg 
different  amounts  of  light,  and  for  the  correction  of  spherical 
and  chromatic  aberration,  could  have  been  formed  by  natural 
selection,  seems,  I  freely  confess,  absurd  in  the  highest  degree. 
"SVlien  it  was  first  said  that  the  sun  stood  still  and  the  world 
turned  round,  the  common-sense  of  mankind  declared  the  doc- 
trine false  ;  Imt  the  old  saying  of  ]  'ox  popxdi^  vox  Dei,  as  every 
j)hilosopher  knows,  cannot  be  trusted  in  science,  lieason  tells 
me,  that  if  numerous  gradations  from  an  imperfect  and  simple 
eye  to  one  jierfect  and  complex,  each  grade  being  useful  to  its 
possessor,  can  be  shown  to  exist,  as  is  certainly  the  case;  if 
further,  the  eye  ever  slightly  varies,  and  the  variations  be  inher- 
ited, as  is  likewise  certainly  the  case ;  and  if  such  variations 
should  ever  be  useful  to  any  animal  under  changing  conditions  of 
life,  then  the  dilliculty  of  believing  that  a  jierfect  and  complex 
eye  could  be  formed  l>y  natural  selection,  though  insuperable 
by  our  imagination,  cannot  be  considered  real.  How  a  nerve 
comes  to  be  S(Misitive  to  light,  hardly  concerns  us  more  than 
how  life  itself  first  originated ;  but  I  may  remark  that,  as  some 


CuAP.  VI.  AND  COMPLICATION.  I79 

of  the  lowest  organisms,  in  Avbich  nerves  cannot  be  detected, 
are  known  to  be  sensitive  to  light,  it  does  not  seem  impossible 
that  certain  elements  in  the  sarcode,  of  which  they  are  mainly 
composed,  should  become  aggregated  and  developed  into  nerves 
endowed  with  this  special  sensibility. 

In  searching  for  the  gradations  through  which  an  organ  in 
any  species  has  been  perfected,  we  ought  to  look  exclusively  to 
its  lineal  progenitors  ;  but  this  is  scarcely  ever  possible,  and  we 
are  forced  to  look  to  other  species  and  genera  of  the  same 
group,  that  is,  to  the  collateral  descendants  from  the  same 
j)arent-form,  in  order  to  see  what  gradations  arc  possible,  and 
for  the  cliance  of  some  gradations  liaving  been  transmitted  in 
an  unaltered  or  little  altered  condition.  But  the  state  of  the 
organ  even  in  distinct  classes  may  incidentally  throw  light  on 
the  steps  hy  which  it  has  been  perfected  in  any  one  species. 

The  simplest  organ  which  can  be  called  an  eye  consists  of 
an  optic  nerve,  surrounded  by  pigment-cells  covered  by  trans- 
lucent skin,  but  without  any  lens  or  other  refractive  body.  AVe 
may,  however,  according  to  M.  Jourdain,  descend  even  a  step 
lower  and  find  aggregates  of  pigment-cells,  apparently  serving 
as  an  organ  of  vision,  but  without  any  nerve,  and  resting  merely 
on  sarcodic  tissue.  Eyes  of  the  above  simple  nature  are  not 
capable  of  distinct  vision,  and  serve  only  to  distinguish  light 
from  darkness.  In  certain  starfishes,  small  depressions  in  the 
layer  of  pigment  which  surrounds  tlie  nerve  are  filled,  as  de- 
scribed by  the  author  just  quoted,  Avith  transparent  gelatinous 
matter,  projecting  with  a  convex  surface,  like  the  cornea  in  the 
higher  animals.  He  suggests  that  this  serves  not  to  form  an 
image,  but  only  to  concentrate  the  luminous  raj's  and  render 
their  perception  more  easy.  In  this  concentration  of  the  rays 
we  gain  the  first  and  by  far  the  most  important  step  toward 
the  formation  of  a  true,  picture-forming  eye  ;  for  we  have  only 
to  place  the  naked  extremity  of  the  optic  nerve,  which  in  some 
of  the  lower  animals  lies  deeply  buried  in  the  body,  and  in 
some  near  the  surface,  at  the  right  distance  from  the  concentrat- 
ing ap]iaratus,  and  an  image  will  be  formed  on  it. 

In  the  great  class  of  tlie  Articulata,  we  may  start  from  an 
optic  nerve  simply  coatccl  with  pigment,  the  latter  sometimes 
forming  a  sort  of  pupil,  but  destitute  of  a  lens  or  other  optical 
contrivance.  "NVitii  insects  it  is  now  known  that  the  numer- 
ous facets  on  the  cornea  of  the  great  comjiound  eyes  form 
true  lenses,  and  that  the  cones  include  curiously-modified 
nervous  filaments.     But  these  organs  in  the  Articulata  are  so 


ISO  ORGANS   OF  EXTKEME  PERFECTION  Chap.  VI. 

mucli  diversified  that  Milller  formerly  made  three  main  chxsses 
of  compound  eyes  -with  seven  subdivisions,  l^esidcs  a  fourth 
main  chiss  of  ag-j^regated  simple  eyes. 

AVhcn  we  reflect  on  these  facts,  here  f^ivcn  too  briefly,  with 
respect  to  the  wide,  diversified,  and  graduated  range  of  struct- 
in-e  in  the  eyes  of  the  lower  animals ;  and  when  we  bear  in 
mind  how  small  the  number  of  all  the  forms  now  living  must 
he  in  comparison  with  those  which  have  become  extinct,  the 
ditliculty  ceases  to  be  very  great  in  believing  that  natural  se- 
lection may  have  converted  the  simple  apparatus  of  an  optic 
nerve,  coated  with  pigment  and  invested  by  transparent  mem- 
brane, into  an  optical  instrument  as  perfect  as  is  possessed  by 
an}'  member  of  the  great  Articulate  Class. 

He  who  will  go  thus  far,  ought  not  to  hesitate  to  go  one 
step  further,  if  he  finds  on  finishing  this  volume  that  large  bod- 
ies of  facts,  otherwise  inexplicable,  can  be  explained  by  the 
theory  of  descent  with  modification  ;  he  ought  to  admit  that  a 
structure  even  as  perfect  as  an  eagle's  eye  might  be  formed  by 
natural  selection,  although  in  tliis  case  he  does  not  know  the 
transitional  states.  It  has  been  objected  that,  in  order  to  mod- 
ify the  eye  and  still  preserve  it  as  a  perfect  instrument,  many 
changes  would  have  to  be  effected  simultaneously,  which,  it  is 
assumed,  could  not  be  done  through  natural  selection  ;  but,  as 
I  have  attempted  to  show  in  my  work  on  the  variation  of  do- 
mestic animals,  it  is  not  necessary  to  suppose  that  all  the  modi- 
fications were  simultaneous,  if  tliey  were  extremely  slight  and 
gradual.  Even  in  the  most  highly-organized  division  of  the 
animal  kingdom,  namely,  the  Vcrtebrata,  we  can  start  from  an 
eye  so  simple,  that  it  consists,  as  in  the  lancelet,  of  a  little 
sack  of  transparent  skin,  furnished  with  a  nerve  and  lined  with 
pigment,  but  destitute  of  any  other  apparatus.  In  both  fishes 
and  reptiles,  as  Owen  has  remarked,  "  the  range  of  gradations 
of  dioptric  structures  is  very  great."  It  is  a  significant  fiict 
that  even  in  man,  according  to  tlie  high  authority  of  Virchow, 
tlic  beautiful  crj^stalline  lens  is  formed  in  tlie  embryo  by  an 
accumulation  of  epidermic  cells,  lying  in  a  sack-like  fold  of  the 
skin ;  and  tlie  vitreous  body  is  formed  from  embryonic  subcu- 
taneous tissue?.  It  is  indeed  indispensable,  in  order  to  arrive  at 
a  just  conclusion  regarding  the  formation  of  the  eye,  with  all 
its  marvellously  perfect  characters,  that  the  reason  should  con- 
quer the  imagination  ;  but  I  have  felt  this  difficulty  far  too 
keenly  to  be  surprised  at  any  degree  of  hesitation  in  extend 
ing  the  principle  of  natural  selection  to  so  startling  a  length. 


CiiAr.  VI.  AND  COMPLICATION.  181 

It  is  scarcely  possible  to  avoid  comparing  tlic  eye  with  a 
telescope.  We  know  tliat  tliis  instrument  lias  been  peri'eeted 
by  the  long-continued  ell'orts  of  the  highest  human  intellects  ; 
and  we  natm-ally  infer  that  the  eye  has  been  formed  by  a  some- 
what analogous  process.  But  may  not  this  inference  be  pre- 
sumptuous ?  Have  we  any  right  to  assume  that  the  Creator 
works  by  intellectual  powers  like  those  of  man?  If  we  must 
compare  the  e^'e  to  an  ojjtical  instrument,  we  ought  in  imagi- 
nation to  take  a  thick  layer  of  transparent  tissue,  with  spaces 
tilled  with  fluid,  and  with  a  nerve  sensitive  to  light  beneatlt, 
and  then  suppose  every  ])art  of  this  layer  to  be  continually 
changing  slowly  in  d(Misity,  so  as  to  separate  into  layers  of 
dillerent  densities  and  thicknesses,  placed  at  different  distances 
from  each  other,  and  with  the  surfaces  of  each  layer  slowly 
changing  in  form.  Further,  Ave  must  suppose  that  there  is  a 
power,  r(>presented  by  natural  selection  or  the  survival  of  the 
Mttest,  always  intently  watching  each  sliglit  alteration  in  the 
transparent  la^'ers  ;  and  carefully  preserving  eaoli  which,  undc^' 
varied  circumstances,  in  any  way  or  in  any  degree,  tends  to 
jiroduce  a  distincter  image.  We  must  suppose  each  new  state 
of  the  instrument  to  be  multiplied  by  the  million;  each  to  be 
preserved  until  a  better  one  is  produced,  and  then  the  old  ones 
to  be  all  destroj-ed.  In  living  bodies,  variation  will  cause  the 
slight  alterations,  generation  will  multiply  them  almost  infi- 
nitely, and  natural  selection  Avill  pick  out  Avith  unerring  skill 
each  improvement.  Let  this  process  go  on  for  millions  of 
years  ;  and  during  each  year  on  millions  of  individuals  of  many 
kinds;  and  may  we  not  believe  that  a  living  optical  instrument 
might  tluis  be  formed  as  superior  to  one  of  glass,  as  the  works 
of  the  Creator  are  to  those  of  man  ? 

Modes  of  Transition. 

If  it  could  be  demonstrated  that  any  com])lex  organ  existed, 
which  could  not  possibly  have  been  formed  by  numerous,  suc- 
cessive, slight  modifications,  my  theor}-  would  absolutely  break 
down.  But  I  can  find  out  no  such  case.  No  doubt  manv  or- 
gans exist  of  which  we  do  not  know  the  transitional  grades, 
more  especially  if  we  look  to  much-isolated  spt^cies,  roimd 
which,  according  to  the  theory,  there  has  been  nujch  extinction. 
Or  again,  if  we  take  an  organ  common  to  all  the  members  of 
a  large  class,  for  in  this  latter  case  the  organ  must  have  been 
originally  fonnod  at  an  extremely  remote  period,  since  which 


1S2  MODES  OF  TRANSITION.  Chap.  VI. 

all  the  mail)'-  members  of  the  class  have  been  developed ;  and, 
iu  order  to  discover  the  early  transitional  grades  through 
which  the  organ  has  passed,  Ave  should  have  to  look  to  very 
ancient  ancestral  forms,  long  since  become  extinct. 

We  should  be  extremely  cautious  in  concluding  that  an  or- 
gan could  not  have  been  formed  by  transitional  gradations  of 
some  kind.  Numerous  cases  could  be  given  among  the  lower 
animals  of  the  same  organ  performing  at  the  same  time  wholly 
distinct  functions  ;  thus  the  alimentary  canal  respires,  digests, 
and  excretes,  in  the  larva  of  the  dragon-fly  and  in  the  fish  Co- 
bites.  In  the  Hydra,  the  animal  may  be  turned  inside  out,  and 
the  exterior  surface  will  then  digest  and  the  stomach  respire- 
In  such  cases  natural  selection  might  specialize,  if  any  advan- 
tage were  thus  gained,  the  whole  or  part  of  an  organ,  Avhich 
had  previously  performed  two  functions,  for  one  function  alone, 
and  thus  by  insensible  steps  greatly  change  its  nature.  Many 
plants  are  known  which  regularly  produce  at  the  same  time 
differently-constructed  flowers  ;  and  if  such  plants  were  to  pro- 
duce one  kind  alone,  a  great  change  would  in  some  cases  be 
effected  in  the  character  of  the  species.  It  can  also  be  shown 
that  the  pi'oduction  of  the  two  sorts  of  flowers  by  the  same 
plant  has  been  effected  by  finely-graduated  steps.  Again,  two 
distinct  organs  in  the  same  individual  may  simultaneously  per- 
form the  same  function,  and  this  is  a  highly-imj^ortant  means 
of  transition :  to  give  one  instance — there  are  fish  with  gills 
or  branchiae  that  breathe  the  air  dissolved  in  the  water,  at  the 
same  time  that  they  breathe  free  air  in  their  swim-bladders, 
this  latter  organ  being  divided  by  highly-vascular  partitions, 
and  having  a  ductus  pneumaticus  for  the  supply  of  air.  To 
give  another  instance  from  the  vegetable  kingdom:  plants 
climb  l^y  three  distinct  means,  by  spirally  twining,  by  clasping 
a  support  with  their  sensitive  tendrils,  and  by  the  emission  of 
aerial  rootlets  ;  tliese  three  means  are  usually  found  in  distinct 
groups,  but  some  few  plants  exhibit  two  of  the  means,  or  even 
all  three,  combined  in  ttie  same  individual.  In  all  such  cases 
one  of  the  two  organs  for  performing  the  same  function  might 
be  modified  and  perfected  so  as  to  ])erf()rm  all  the  work,  being 
aided  during  the  progress  of  modification  by  the  other  organ ; 
and  then  this  other  organ  might  be  modified  for  some  other 
and  quite  distinct  purpose,  or  be  wholly  obliterated. 

The  illustration  of  the  swim-l)ladder  in  fishes  is  a  good  one, 
becausi?  it  shows  us  clearly  the  higher  important  fact  that  an 
organ  originally  constructed  for  one  purpose,  namely  flotation, 


CiiAr.  VI.  JIODES  OF  TRANSITION.  183 

may  be  converted  into  one  for  a  widcly-tliffercnt  purpose, 
namely,  respiration.  Tlie  swim-bladder  has,  also,  been  worked 
in  as  an  accessory  to  the  auditory  org'ans  of  certain  hsh.  All 
physiolog^ists  admit  that  the  swim-bladder  is  homologous,  or 
"ideally  similar"  in  position  and  structure  with  the  lungs  of 
the  higher  vertebrate  animals :  hence  there  is  no  reason  to 
doubt  that  the  swim-bladder  has  actually  been  converted  into 
lungs,  or  an  organ  used  exclusively  for  respiration. 

According  to  this  view  it  may  be  inferred  that  all  vertebrate 
animals  with  true  lungs  have  descended  by  ordinary  generation 
from  an  ancient  and  unknown  prototype,  which  was  furnished 
witii  a  floating  apparatus  or  swim-bladder.  We  can  thus,  as  I 
infer  from  Owen's  interesting  description  of  these  parts,  under- 
sta,nd  the  strange  fact  that  every  particle  of  food  and  drink 
which  we  swallow  has  to  pass  over  the  orifice  of  the  trachi^a, 
with  some  risk  of  falling  into  the  lungs,  notwithstanding  the 
beautiful  contrivance  by  which  the  glottis  is  closed.  In  the 
higlier  Vertebrata  the  branchiaj  have  wholly  disappeared — but 
in  the  embryo  the  slits  on  the  sides  of  the  neck  and  the  loop- 
like course  of  the  arteries  still  mark  tlunr  former  position.  But 
it  is  conceivable  that  the  now  utterly  lost  branchiae  might  have 
been  gradually  worked  in  by  natural  selection  for  some  distinct 
purpose  :  for  instance,  the  branchiir;  and  dorsal  scales  of  Anne- 
lids are  believed  to  be  homologous  with  the  wings  and  wing- 
covcrs  of  insects,  and  it  is  not  improbable  that  with  our  existing 
insects  organs,  which  at  an  ancient  period  served  for  respiration, 
have  actually  been  converted  into  organs  of  flight. 

In  considering  transitions  of  organs,  it  is  so  important  to 
bear  in  mind  the  probability  of  conversion  from  one  function  to 
another,  that  I  will  give  another  instance.  Pedunculated  cir- 
ripcdes  have  two  minute  folds  of  skin,  called  by  me  the  ovigerous 
frena,  Avhidi  serve,  through  the  means  of  a  sticky  secretion,  to 
retain  the  eggs  until  they  are  hatched  within  the;  sack.  These 
cirri|)edes  have  no  branclu;ii,  the  whole  surface  of  the  body  and 
of  the  sack,  together  with  the  small  frena,  serving  for  respira- 
tion. Tiic  13alanid;\3  or  sessih;  cirripedes,  on  the  other  hand, 
have  no  ovigerous  frena,  the  eggs  lying  loose  at  the  bottom  of 
the  sack,  within  the  well-enclosed  shell ;  but  they  iiave,  in  the 
same  relative  position  with  the  frena,  large,  much-fokU'd  mem- 
branes, which  freely  communicate  with  the  circulatory  lacunixj 
of  the  sack  and  body,  and  which  have  been  considered  to  be 
branchiaj  by  Prof.  Owen  and  by  all  other  naturalists  who  have 
treated  on  the  sul)ject.     Now  I  think  no  one  will  dispute  that 


184  DIFFICULTIES   OF   THE  THEORY  Chap.  VI. 

the  ovigcrous  frcna  in  the  one  family  arc  strictly  homologous 
■with  the  braiicliiiu  of  tlic  other  family;  indeed,  they  graduate 
into  each  other.  Therefore  it  need  not  be  doubted  that  the 
two  little  folds  of  skin,  -which  originally  served  as  ovigerous 
frena,  but  -which,  likewise,  very  slightly  aid  in  the  act  of  res- 
piration, have  been  gradually  con\erte(l  by  natural  selection 
into  branchije,  simply  through  an  increase  in  their  size  and  the 
obliteration  of  their  adhesive  glands.  If  all  pedunculated  cir- 
rijiedes  had  become  extinct,  and  they  have  already  suffered  far 
more  extinction  than  have  sessile  cirripedes,  who  Avonld  ever 
have  imagined  that  the  branchioi  in  this  latter  family  had 
originally  existed  as  organs  for  pre\'cnting  the  ova  from  being 
washed  out  of  the  sack  ? 

iSj^ecial  Difficulties  of  the,  Theory  of  Natural  Selection. 

Although  -we  must  be  extremely  cautious  in  concluding 
that  any  organ  could  not  have  been  produced  by  successive 
transitional  gradations,  yet  vmdoubtedly  serious  cases  of  difli- 
culty  occur,  some  of  which  will  be  discussed  in  my  fiiture  work. 

One  of  the  most  serious  is  that  of  neuter  insects,  which  are 
often  diiFcrently  constructed  from  either  the  males  or  fertile 
females;  but  this  case  will  be  treated  of  in  the  next  chapter. 
Tlie  electric  organs  of  fishes  offer  another  case  of  special  diffi- 
culty ;  for  it  is  impossible  to  conceive  by  what  steps  these 
Avondrous  organs  have  been  produced.  As  Owen  has  remarked, 
there  is  much  analogy  between  them  and  ordinary  muscles,  in 
their  manner  of  action,  in  the  influence  on  them  of  the  nervous 
power  and  of  stimulants  svich  as  strychnine,  and  as  some  be- 
lieve in  their  intimate  structure.  M^e  do  not  even  know  of 
-what  use  these  organs  are ;  though  in  the  Gjinnotus  and  Tor- 
pedo they  no  doubt  serve  as  powerful  means  of  defence  and 
perhaps  for  securing  prey;  3'et  in  the  Kay  an  analogous  organ 
in  the  tail,  even  when  greatly  irritated,  manifests,  as  lately 
observed  by  Matteuccu,  but  little  electricity — so  little  that  it 
can  hardl}^  be  of  use  for  such  purposes.  ^Moreover,  in  the  Kay, 
besides  the  organ  just  referred  to,  there  is,  as  Dr.  K.  ^McDonnell 
has  shown,  another  organ  near  the  head,  not  known  to  be  elec- 
trical, but  which  appears  to  be  the  real  homologue  of  the  elec- 
tric batter}'  in  the  torpedo.  Lastly,  as  we  know  nothing  about 
the  lineal  progenitors  of  these  fishes,  it  must  be  admitted  that 
we  are  too  ignorant  to  be  enabled  to  aflirm  that  no  transitions 
arc  possible,  through  which  the  electric  organs  might  have 
been  developed. 


CiiAi-.  YI.  OF  NATURAL  SELECTION.  185 

Tliesc  same  organs  at  first  appear  to  offer  anotncr  and  far 
more  serious  difficulty ;  for  they  occur  in  about  a  dozen  kinds 
of  fisli,  of  Avliich.  several  arc  Avidely  remote  in  their  affinities. 
Generally  when  the  same  organ  is  found  in  several  niemhers 
of  the  same  class,  especially  if  in  mc^mbers  having  very  differ- 
ent habits  of  life,  we  may  attribute  its  presence  to  inheritance 
from  a  common  ancestor;  and  its  absence  in  some  of  the  mem- 
bers to  loss  through  disuse  or  natural  selection.  So  that,  if 
the  electric  organs  had  been  inherited  from  some  one  ancient 
progenitor,  we  might  have  expected  that  all  electric  fishes 
would  have  been  specially  related  to  each  other;  but  this  is 
far  from  the  case.  Nor  does  geology  at  all  lead  to  the  Ijclief 
that  most  fishes  formerly  possessed  electric  organs,  which  their 
modified  descendants  have  now  lost.  But  when  we  look  at 
the  subject  more  closely,  wc  find  in  the  several  fishes  provided 
with  electric  organs  that  these  are  situated  in  diiferent  parts 
of  the  body — that  they  differ  in  construction,  as  in  the  arrange- 
ment of  the  plates,  and  according  to  Pacini,  in  the  process  or 
means  by  which  the  electricity  is  excited — and  lastly,  in  the 
requisite  nervous  power  being  supplied  through  different  nerves 
from  widely-diffi;rent  sources,  and  this  is  perhaps  the  most  im- 
])ortant  of  all  the  diflerences.  Hence  in  the  several  remotely- 
atlied  fishes  furnished  with  electric  organs,  these  cannot  be 
ccnisidered  as  homologous,  but  only  as  analogous  in  function. 
Consequently  there  is  no  reason  to  suppose  that  they  have 
been  inherited  from  a  common  progenitor ;  for,  had  this  been 
the  case,  they  would  have  closely  resembled  each  other  in  all 
respects.  Thus  tlic  greater  difficulty  disappears,  leaving  only 
the  lesser  yet  still  great  difliculty  ;  namely,  by  what  graduated 
steps  these  organs  have  arisen  and  been  develojied  in  each  sepa- 
rate grouji  of  fishes. 

Tiic  luminous  organs  which  occur  only  in  a  few  insects, 
belonging  to  widely-different  fiunilies  and  orders,  and  v.hich 
arc  situated  in  different  jiarts  of  the  body,  offer  a  difficidty 
almost  exactly  jiaralhd  witli  tiiat  of  the  electric  organs.  Other 
cases  could  be  given;  for  instance,  in  plants,  the  very  curious 
contrivance  of  a  mass  of  pollen-grains,  borne  on  a  foot-stalk 
with  an  adhesive  gland,  is  apparently  the  same  in  Orchis  and 
Asclcpias — genera  almost  as  remote  as  is  possible  among 
flowering  ])lants.  In  all  such  cases  of  two  species,  fiir  removed 
from  each  other  in  the  scale  of  organization,  being  furnislied 
with  similar  anomalous  organs,  it  should  be  observed  that,  al- 
though the  general  appearance  and  function  of  the  organ  may 


180  DIFFICULTIES   OF  THE  THEORY  Ciur.  VI. 

1)0  iilcMitically  the  saiiie,  yet  some  fundamental  difference  be- 
tween them  can  always,  or  almost  always,  be  detected.  I  am 
inclined  to  believe  that,  in  the  same  manner  as  two  inen  have 
sometimes  independently  hit  on  the  same  invention,  so  natural 
selection,  working  for  tlie  good  of  each  being  and  taking  ad- 
vantage of  analogous  variations,  has  sometimes  modified  in 
nearly  the  same  way  two  organs  in  two  distinct  organic  beings, 
which  owe  but  little  of  tlieir  structure  in  common  to  inheritance 
from  a  common  progenitor. 

Fritz  MllUcr,  in  a  remarkable  work  recently  published,  has 
investigated  a  nearly  parallel  case,  in  order  to  test  the  views 
advanced  in  this  volume.  Several  families  of  crustaceans  in- 
clude a  few  species  which  possess  an  air-breathing  apparatus, 
and  are  fitted  to  live  out  of  the  water.  In  two  of  these  fam- 
ilies, which  -were  more  especially  examined  by  Miiller,  and 
which  are  nearly  related  to  each  other,  the  species  agree  most 
closely  in  all  important  characters  ;  namely,  in  their  sense-or- 
gans, circulating  system,  in  the  position  of  the  tufts  of  hair 
with  whicli  their  complex  stomachs  arc  lined,  and  lastly  in  the 
v/hole  structure  of  the  Avater-breatliing  Ijranchia^,  even  to  the 
microscopical  hooks  by  Avhich  they  arc  cleansed.  Hence  it 
might  have  been  expected  that  the  equally  important  air- 
breathing  apparatus  would  have  been  the  same  in  the  fevv^ 
species  in  both  families  Avhich  live  on  the  land ;  and  this  might 
Iiavc  been  tlie  more  confidently  expected  by  those  wlio  believe 
in  distinct  creations ;  for  why  sliould  this  one  apparatus,  given 
for  the  same  special  piu^ose  to  these  species,  have  been  made 
to  differ,  Avhile  all  the  other  important  organs  are  closely  simi- 
lar or  rather  identical  ? 

Fritz  Mllller  argues  that  this  close  similarity  in  so  many 
points  of  structure  must,  in  accordance  with  the  views  ad- 
vanced by  me,  be  accounted  for  by  inheritance  from  a  common 
progenitor.  But  as  the  vast  majority  of  the  species  in  tlie 
above  two  families,  as  well  as  most  crustaceans  of  all  orders, 
are  aquatic  in  their  habits,  it  is  improbable  in  the  highest  degree, 
that  their  common  progenitor  should  have  been  adapted  for 
breathing  air.  Miiller  was  thus  led  carefully  to  examine  the 
apparatus  in  the  air-breathing  species;  and  in  each  he  found 
it  to  diffor  in  several  important  points,  as  in  the  position  of  the 
orifices,  in  the  manner  in  which  they  are  opened  and  closed, 
and  in  some  accessory  details.  Now  such  differences  are  intelli- 
gible, and  might  even  have  been  anticipated,  on  the  siip]iositi<-)n 
that  species  belonging  to  distinct  families  had  slowly  become 


Chap.  VI.  OF  NATURAL  SELECTION.  1S7 

adapted  to  live  more  and  more  out  of  "water,  and  to  breathe 
the  air.  For  these  species,  from  beloiif^ing  to  distinct  families, 
■would  difler  to  a  certain  extent,  and  in  accordance  with  the 
principle  that  the  nature  of  each  variation  depends  on  two  fac- 
tors, viz.,  the  nature  of  the  orp^anism  and  that  of  the  condi- 
tions, the  variability  of  these  crustaceans  assuredly  would  not 
have  been  exactly  the  same.  Consequently  natural  selection 
would  have  had  diiTerent  materials  or  variations  to  work  on,  in 
order  tu  arrive  at  the  same  functional  result;  and  the  structures 
thus  acquired  would  almost  necessarily  have  dillered.  On  the 
hypotliesis  of  6C]>arate  acts  of  creation  the  whole  case  remains 
unintelli,Lrible.  The  above  line  of  arn^mcnt,  as  advanced  by 
Fritz  Miiller,  seems  to  have  had  j^reat  weiglit  in  leadino^  this 
distin<^uislicd  naturalist  to  accept  the  views  maintained  by  me 
in  this  volume. 

•  In  the  several  cases  just  discussed,  wc  have  seen  that  in 
beings  more  or  less  remotely  allied,  the  same  end  is  gained 
and  the  same  function  performed  by  organs  in  appearance, 
though  not  in  truth,  closely  similar.  But  the  common  rule 
throughout  Nature  is  that  the  same  end  is  gained,  even  some- 
times in  the  case  of  beings  closely  related  to  each  other,  by  the 
most  diversified  means.  How  differently  constructed  is  the 
feathered  wing  of  a  bird  and  the  membrane-covered  yying  of  a 
l)at  with  all  the  digits  largely  developed ;  and  still  more  so  the 
four  Avings  of  a  butterfly,  the  two  wings  of  a  fly,  and  the  two 
wings  of  a  beetle,  together  with  the  elytra !  13ivalve  shells 
are  made  to  open  and  shut,  but  on  what  a  immber  of  ])atterns 
is  the  hinge  constructed,  from  the  long  row  of  neatly  inter- 
locking teetli  in  a  Nucula  to  the  simple  ligament  of  a  Mussel ! 
tSeeds  arc  disseminated  by  their  minuteness — by  their  capsule 
being  converted  into  a  light  balloon-like  envelope — by  being- 
embedded  in  pulp  or  flcsli,  formed  of  tlie  most  diverse  parts, 
and  rendered  nutritious,  as  well  as  conspicuously  colored,  so  as 
to  attract  and  be  devoured  by  birds — ])y  having  hooks  and 
grapnels  of  many  kinds  and  serrated  awns,  so  as  to  adhere  to 
the  fur  of  quadmpeds — and  by  being  furnish(>d  Avith  wings  and 
plumes,  as  different  in  shape  as  elegant  in  structure,  so  as  to 
be  wafted  by  every  breez(\  I  will  give  one  other  instance ; 
for  this  subject  of  the  same  end  being  gained  by  the  niost  di- 
versified means  well  deserves  attention.  Some  authors  main- 
tain that  organic  beings  have  been  formed  in  many  ways  for 
the  sake  of  mere  variety,  almost  like  toys  in  a  shop,  but  such  a 


188  DIFFICULTIES  OF  THE  THEOKY  Chap.  VI. 

view  of  Nature  is  incrediljlo.  Witli  plants  having'  scjiarated 
Bcxcs,  and  witli  those  in  whicli,  tlious-li  herniaplnodites,  the 
pollen  docs  not  spontaneously  fall  on  tlie  stig'ma,  some  aid  is 
necessary  for  their  fertilization.  AVith  several  kinds  this  is 
cHected  by  the  polli'U-yrains,  which  are  lig'ht  and  incoherent, 
Ix'ino;  blown  1)y  the  wind  through  mere  chance  on  to  the  stigma  ; 
and  this  is  the  simj)lest  plan  which  can  well  be  conceived. 
An  almost  equally  simple,  though  very  different,  plan  occurs 
in  many  plants  in  which  a  symmetrical  flower  secretes  a  few 
drops  of  nectar,  and  is  consequently  visited  by  insects ;  and 
these  carry  the  pollen  from  the  anthers  to  the  stigma. 

From  this  simple  stage  we  may  pass  through  an  inexhaust- 
ible number  of  contrivances,  all  for  the  same  purpose  and 
cflected  in  essentially  the  same  manner,  but  entailing  changes 
in  every  part  of  the  llower.  The  nectar  may  be  stored  in  vari- 
ously-shaped receptacles,  with  the  stamens  and  pistils  modi- 
fied in  many  ways,  sometimes  forming  traj)-like  contrivances, 
and  sometimes  capable  of  neatly-adapted  movements  through 
irritability  or  elasticity.  From  such  structures  we  may  ad- 
vance till  Ave  come  to  such  a  case  of  extraordinary  adaptation 
as  that  lately  described  by  Dr.  Crugcr  in  the  Coryanthcs.  Tliis 
orchid  has  jiart  of  its  labellum  or  lower  lip  hollowed  out  into 
a  great  bucket,  into  which  drops  of  almost  pure  water  contin- 
ually fall  from  two  secreting  horns  which  stand  above  it ;  and 
v.hen  the  bucket  is  half  full,  the  water  overflows  by  a  spout 
on  one  side.  The  basal  part  of  the  labellum  stands  over  the 
bucket,  and  is  itself  hollowed  out  into  a  sort  of  chamber  with 
two  lateral  entrances ;  Avithin  tliis  chamber  there  are  curious 
fleshy  ridges.  The  most  ingenious  man,  if  he  had  not  Avit- 
nessed  Avhat  takes  ])lace,  could  never  liaA^e  imagined  Avhat  pur- 
pose all  these  parts  serve.  But  Dr.  Crtiger  saAV  croAvds  of 
large  humble-bees  A'isiting  the  gigantic  flowers  of  this  orchid, 
not  in  order  to  suck  nectar,  but  to  gnaAV  ofi"  the  ridges  Avithin 
the  chamber  aboA^e  the  bucket ;  in  doing  this  they  frequently 
I)ushe(l  each  other  into  the  bucket,  and  their  wings  being  thus 
Avetted  they  could  not  fly  away,  liut  had  to  craAvl  out  through 
the  passage  formed  by  tlie  spout  or  OA-erflow.  Dr.  Crllger  saw 
a  "continual  procession"  of  bees  thus  crawling  out  of  their  in- 
A'oluntary  bath.  The  passage  is  narroAver,  antl  is  roofed  over 
by  the  column,  so  that  a  bee,  in  forcing  its  Avay  out,  first  rubs 
its  back  against  the  viscid  stigma  and  then  against  the  viscid 
glands  of  the  pollen-masses.  The  jiollen-masses  are  thus  glued 
to  the  back  of  that  bee  Avhich  first  happens  to  craAvl  out  through 


CiiAP.  VI.  OF  NATURAL  SELECTION.  189 

the  passage  of  a  litely-cxpandcd  flower,  and  arc  thus  carried 
away.  Dr.  Cril<^('r  sent  ine  a  (lower  in  spirits  of  wine,  with  a 
bee  which  he  liad  killed  before  it  liad  ([uite  crawled  ont  with  a 
pollen-mass  still  fastened  to  its  back.  When  the  bee,  thus 
provided,  (lies  to  another  (lower,  or  to  the  same  flower  a  sec- 
ond time,  and  is  jnished  by  its  comrades  into  the  bucket  and 
then  crawls  out  by  the  iiassag-e,  the  pollen-mass  necessarily 
comes  first  into  contact  with  the  viscid  stig'ma,  and  adheres  to 
it,  and  the  (lower  is  fertilized.  Now  at  last  we  see  the  full 
use  of  every  part  of  the  flower,  of  the  water-secreting  horns, 
of  the  bucket  half  full  of  water,  wliicli  prevents  the  bees  from 
flving  away  and  forces  them  to  crawl  out  through  the  spout, 
and  lub  against  the  properly-placed  viscid  pollen-masses  and 
viscid  stigma. 

The  construction  of  tlie  (lower  in  another  closely-allied  or- 
chid, namely,  the  Catasetum,  is  widely  dilVerent,  though  serving 
the  same  end;  and  is  equally  curious.  Bees  visit  these  flow- 
ers, like  those  of  the  Coryanthes,  in  order  to  gnaw  the  label- 
lum ;  in  doing  this  they  inevitably  touch  a  long,  tapering, 
sensitive  projection,  or,  as  I  have  called  it,  the  antenna.  This 
antenna,  when  touched,  transmits  a  sensation  or  vibration  to  a 
certain  membrane  which  is  instantly  ruptured ;  this  sets  free 
a  spring  by  which  the  pollen-mass  is  shot  forth,  like  an  arrow, 
in  the  right  direction,  and  adheres  by  its  viscid  extremity''  to 
the  back  of  the  bee.  The  pollen-mass  of  a  male  plant  is  thus 
carried  to  the  flower  of  a  female  plant,  where  it  is  brought  into 
contact  with  the  stigma,  which  is  A'iscid  enough  to  break  cer- 
tain elastic  threads,  and,  retaining  the  pollen,  fertilization  is 
elTected. 

How,  it  may  be  asked,  in  the  foregoing  and  in  innumerable 
other  instances,  can  we  imderstand  the  graduated  scale  of 
complexity  and  the  multifarious  means  for  gaining  the  same 
end  V  The  answer  no  doubt  is,  as  already  remarked,  that  when 
two  forms  vary,  which  already  diller  from  each  other  even  in  a 
slight  degree,  tht;  variability  will  not  be  of  the  same  exact  na- 
ture, and  conseciuently  the  results  obtained  through  natural 
selection  for  the  same  general  ])urpose  will  not  be  the  same. 
We  should  also  bear  in  mind  that  every  highly-developed  or- 
ganism has  passed  through  a  long  course  of  modilication;  and 
that  each  moditied  structure  tends  to  be  inherited,  so  that  it 
will  not  readily  be  wholly  lost,  but  may  be  modified  again  and 
again.  Hence  the  structure  of  each  part  of  each  species,  for 
whatever  purpose  used,  is  the  sum  of  the   many  inherited 


100  OEGANS   OF  LITTLE  IMPORTANCE  Chap.  VL 

changes,  through  which  that  species  has  passed  during  its  suc- 
cessive adaptations  to  changed  habits  and  conditions  of  life. 

Finally,  then,  although  in  many  cases  it  is  most  difficult 
even  to  conjecture  by  what  transitions  many  organs  have  ar- 
rived at  their  present  state;  yet,  considering  how  small  the 
proportion  of  living  and  known  forms  is  to  the  extinct  and  un- 
known, I  have  been  astonished  how  rarely  an  organ  can  be 
named,  toward  which  no  transitional  grade  is  known  to  lead. 
It  certainly  is  true  that  new  organs,  appearing  as  if  specially 
created  for  some  purjDOse,  rarely  or  never  appear  suddenly  in 
any  class ;  as  indeed  is  sho^\'n  by  that  old,  but  somewhat  ex- 
aggerated, canon  in  natural  history  of  "  Natura  non  facit  sal- 
tum."  Vio  meet  with  this  admission  in  the  writings  of  almost 
every  experienced  naturalist ;  or,  as  Milne  Edwards  has  well 
expressed  it,  Nature  is  prodigal  in  variety,  but  niggard  in  inno- " 
vation.  Why,  on  the  theory  of  Creation,  should  there  be  so 
much  variety  and  so  little  novelty  ?  "Why  should  all  the  parts 
and  organs  of  many  independent  beings,  each  supposed  to 
have  been  separately  created  for  its  proper  place  in  Nature, 
be  so  commonly  linked  together  by  graduated  steps  ?  Why 
should  not  Nature  take  a  sudden  leap  from  structm-e  to  struct- 
ure ?  On  the  theory  of  natural  selection,  we  can  clearly  un- 
derstand why  she  should  not;  for  natural  selection  acts  only 
by  taking  advantage  of  slight  successive  variations ;  she  can 
never  take  a  sudden  leap,  but  must  advance  by  short  and  sure 
though  slow  steps. 

Organs  of  little  apparent  Importance^  as  affected  by  Natural 
Selection. 

As  natural  selection  acts  by  life  and  death — by  the  survival 
of  the  fittest,  and  by  the  destruction  of  the  less  wcll-litted  indi- 
viduals— I  have  sometimes  felt  great  dilllculty  in  understand- 
ing the  origin  or  formation  of  parts  of  little  importance ;  al- 
most as  great,  though  of  a  very  different  kind,  as  in  the  case 
of  the  most  perfect  and  complex  organs. 

In  the  fii-st  place,  we  are  much  too  ignorant  in  regard  to 
the  whole  economy  of  any  one  organic  being,  to  say  what 
slight  modifications  would  be  of  importance  or  not.  In  a  for- 
mer chapter  I  have  given  instances  of  very  trifling  characters, 
such  as  tlie  down  on  fruit  and  the  color  of  its  ilesh,  the  color 
of  the  skin  and  hair  of  quailrupeds,  which,  from  being  corre- 
lated with  constitutional  differences  or  from  determining  the 


Chap.  VI.  AFFECTED  BY  NATURAL  SELECTION.  191 

attacks  of  insects,  mif^lit  assuredly  he  acted  on  by  natural  se- 
lection. Tlie  tail  of  tiie  g^iraffc  looks  like  an  artificially-con- 
structed fly-flapper;  and  it  seems  at  first  incredible  that  tliis 
could  have  been  adapteil  for  its  present  purpose  by  successive 
slight  niodiiications,  each  better  and  better  lifted,  for  so  triliino; 
an  object  as  to  drive  away  flies ;  yet  avc  should  pause  before 
being  too  positive  even  in  this  case,  for  we  know  that  the  dis- 
tribution and  existence  of  cattle  and  other  animals  in  South 
America  absolutely  depend  on  their  power  of  resisting  the  at- 
tacks of  insects  :  so  that  individuals  which  could  by  any  means 
defend  themselves  from  these  small  enemies,  would  be  able  to 
range  into  new  pastures  and  thus  gain  a  great  advantage.  It 
is  not  that  the  larger  (juadrupeds  are  actually  destroyed  (exceiDt 
in  some  rare  cases)  by  flies,  but  they  are  incessantly  harassed 
and  their  strength  reduced,  so  that  they  are  more  subject  to 
disease,  or  not  so  well  enabled  in  a  coming  dearth  to  search 
for  food,  or  to  escape  from  beasts  of  pre}'. 

Organs  now  of  trifling  importance  have  probably  in  some 
cases  been  of  high  imjiortance  to  an  early  progenitor,  and, 
after  having  been  slowly  perfected  at  a  former  period,  have 
been  transmitted  to  existing  species  in  nearly  the  same  state, 
although  now  of  ver}'  slight  use ;  but  any  actually  injurious 
deviations  in  their  structure  will  of  course  have  been  checked 
by  natiu'al  selection.  Seeing  how  important  an  organ  of  loco- 
motion the  tail  is  in  most  aquatic  animals,  its  general  prcsenco 
and  use  for  many  purposes  in  so  many  land  animals,  which  in 
their  lungs  or  modified  swim-bladders  betray  their  aquatic  ori- 
gin, may  perhaps  be  thus  accounted  for.  A  well-developed 
tail  having  been  formed  in  an  aquatic  animal,  it  might  subse- 
quently come  to  be  worked  in  for  all  sorts  of  purposes,  as  a  Ily- 
flapper,  an  organ  of  prehension,  or  as  an  aid  in  turning,  as  with 
the  dog,  though  the  aid  in  this  latter  respect  nuist  be  slight, 
for  the  hare,  with  hardly  any  tail,  can  double  cjuickly  eTiough. 

In  the  second  ])lace,  ^ve  may  sometimes  wrongly  attribute 
im]X)rtance  to  characters  which  have  originated  from  quiti;  sec- 
ondary causes,  independently  of  natural  selection.  We  should 
remember  that  climate,  food,  etc.,  probably  have  had  some, 
])erhaps  a  considerable,  direct  influence  on  the  organization  ; 
that  characters  reajjpear  from  the  law  of  reversion ;  that  ct>r- 
relation  is  an  important  element  of  change;  and  finallv,  that 
sexual  selection  has  often  largely  modified  the  external  i-Iiarac- 
ters  of  the  higher  animals,  so  as  to  give  one  male  an  advantage 
in  fighting  witli  other  males,  or  in  charming  the  female ;  and 


192  ORGA^'S  OF  LITTLE  LMPOKTANCE  Chap.  VL 

characters  gained  through  sexual  selection  may  be  transmitted 
to  both  sexes.  Moreover,  a  modification,  caused  in  any  of  tlic 
above  specified  ways,  may  at  first  have  been  of  no  direct  ad- 
vantage to  a  species,  ])ut  may  subsequently  have  been  taken 
advantage  of  by  its  descendants  under  new  conditions  of  life 
and  newly-acquired  luibits. 

If,  for  instance,  green  woodpeckers  alone  had  existed,  and 
"\ve  did  not  know  that  there  Avere  many  black  and  pied  kinds, 
I  dare  say  that  we  should  have  thought  that  the  green  color 
was  a  beautiful  adaptation  to  hide  this  tree-frequenting  bird 
from  its  enemies  ;  and  consequently  that  it  was  a  character  of 
importance  and  had  been  acquired  through  natural  selection ; 
as  it  is,  the  color  is  probably  in  chief  part  due  to  sexual  selec- 
tion. A  trailing  palm  in  the  Malay  Archipelago  climbs  tlie 
loftiest  trees  by  the  aid  of  exquisitely-constructed  hooks  clus- 
tered around  the  ends  of  the  branches,  and  this  contrivance, 
no  doubt,  is  of  the  highest  service  to  the  plant ;  but  as  we  see 
nearly  similar  hooks  on  many  trees  which  are  not  climbers, 
and  which  there  is  reason  to  l:)elieve,  from  tlie  distribution  of 
the  thorn-bearing  species  in  Africa  and  South  America,  serves 
as  a  defence  against  browsing  quadrupeds,  so  tlie  hooks  on  the 
palm  may  first  have  been  developed  for  this  object,  and  subse- 
quently been  taken  advantage  of  by  the  plant  as  it  imderwent 
further  modification  and  became  a  climber.  The  naked  skin 
on  the  head  of  a  vulture  is  generally  considered  as  a  direct 
adaptation  for  wallowing  in  putridity ;  and  so  it  may  be,  or  it 
may  possibly  be  due  to  tlie  direct  action  of  putrid  matter ;  but 
we  should  be  very  cautious  in  drawing  any  such  inference, 
when  we  see  that  the  skin  on  the  head  of  the  clean-feeding 
male  Turkey  is  likewise  naked.  The  sutures  in  the  skulls  of 
young  mammals  have  been  advanced  as  a  beautiful  adapta- 
tion for  aiding  parturition,  and  no  doubt  they  facilitate,  or  may 
be  indispensable  for  this  act ;  but  as  sutures  occur  in  the  skulls 
of  young  birds  and  reptiles,  Avliich  have  only  to  escape  from 
a  broken  C(i;ji:,  we  may  infer  that  this  structure  has  arisen  from 
the  laws  of  growth,  and  has  been  taken  advantage  of  in  the 
parturition  of  the  higher  animals. 

We  are  profoundly  ignorant  of  the  cause  of  each  slight  va- 
riation or  individual  diflbrence ;  and  we  are  immediately  made 
conscious  of  this  by  reflecting  on  the  diiferences  in  the  breeds 
of  our  domesticated  animals  in  different  countries — more  espc- 
ially  in  the  less  civilized  countries  where  there  has  been  but 
littie  methodical  selection.     Animals  kept  by  savages  in  difler- 


Chap.  YI.  AFFECTED  BY  NATUKAL  SELECTION.  193 

ent  countries  often  have  to  struggle  for  their  own  subsistence, 
and  are  exposed  to  a  certain  extent  to  natural  selection,  and 
individuals  witli  sliglitly-dillerent  constitutions  would  succeed 
best  under  dilTerent  climates.  A  good  observer  states  tliat  in 
cattle  susceptibility  to  the  attacks  of  flies  is  correlated  with 
color,  as  is  the  liability  to  be  poisoned  by  certain  plants ;  so 
that  even  color  would  be  thus  subjected  to  the  action  of  nat- 
ural selection.  Other  observers  are  convinced  that  a  damp 
climate  affects  the  growth  of  the  hair,  and  tliat  with  the  hair 
the  horns  are  correlated.  Mountain-breeds  alwaj-s  differ  from 
lowland-breeds ;  and  a  mountainous  country  would  probably 
affect  the  hind-limbs  fmm  exercising  them  more,  and  possibly 
even  the  form  of  the  jielvis ;  and  then,  by  the  law  of  homolo- 
gous variation,  the  fiont-liml)s  and  the  head  would  probably  be 
affected.  Tlie  shape,  also,  of  the  pelvis  might  affect  by  press- 
ure the  shape  of  certain  parts  of  the  young  in  the  womb. 
The  laborious  breathing  necessary  in  high  regions  would,  we 
have  reason  to  believe,  increase  the  size  of  the  chest ;  and 
again- correlation  would  come  into  play.  The  effects  on  the 
whole  organization  of  lessened  exercise,  together  with  abun- 
dant food,  is  probably  still  more  important ;  and  this,  as  H.  von 
Nathusius  has  lately  shown  in  his  excellent  Treatise,  is  appar- 
ently one  chief  cause  of  the  great  modilication  which  the 
breeds  of  swine  have  undergone.  But  Ave  are  far  too  ignorant 
to  speculate  on  the  relative  importance  of  the  several  known 
and  unknown  causes  of  variation ;  and  I  have  made  these 
remarks  only  to  show  that,  if  Ave  are  unable  to  account  for  the 
characteristic  differences  of  our  domestic  breeds,  which  never- 
theless are  generally  admitted  to  have  arisen  through  ordinary 
generation  from  one  or  a  few  parent-stocks,  we  ought  not  to 
lay  too  much  stress  on  our  ignorance  of  the  precise  cause  of 
the  sliglit  analogous  differences  between  species.  I  might 
have  adduced  for  this  same  purpose  the  dilferences  between 
the  races  of  man,  which  are  so  strongly  marked ;  I  may  add 
that  some  light  can  apparently  be  thrown  on  these  differences, 
through  sexual  selection  of  a  particular  kind,  but  without 
entering  on  full  details  my  reasoning  Avould  appear  frivolous. 

Uillliarian  Doctrine  howfac  true:  JJcauti/  /tow  acquired. 

The  foregoing  remarks  lead  me  to  say  a  few  Avords  on  the 
protest,  lately  made  by  some  naturalists,  against  th«>  utilitarian 
doctrine  that  CA'cry  detail  of  structure  has  been  produced   for 
9 


191       •    UTILITARIAN  DOCTRINE  IIOW  FAR  TRUE:        Chap.  VI. 

the  good  of  its  possessor.  Tliey  believe  that  many  structures 
have  been  created  for  l)eauty  in  the  eyes  of  man,  or,  as  already 
discussed,  for  the  sake  of  mere  variety.  Such  doctrines,  if 
true,  Avould  be  aljsolulely  fatal  to  my  theory.  Yet  I  fully 
admit  that  many  structures  are  now  of  no  direct  use  to  their 
possessors,  and  may  never  have  been  of  an}-  use  to  their  pro- 
genitors. No  doubt,  as  recently  remarked,  the  definite  action 
of  changed  conditions,  correlated  variation,  and  reversion,  have 
all  produced  their  efTects.  But  the  most  important  consider- 
ation is  that  the  chief  part  of  the  organization  of  every  liv- 
ing creature  is  simply  due  to  inheritance;  and  consequently, 
though  each  assuredly  is  well  fitted  for  its  place  in  Nature, 
many  structures  now  have  no  direct  relation  to  existing  habits 
of  life.  Thus,  we  can  hardly  believe  that  the  webbed  feet  of 
the  upland  goose  or  of  the  frigate-bird  are  of  special  use  to 
these  birds ;  we  cannot  believe  that  the  similar  bones  in  the 
arm  of  the  monkey,  in  the  fore-leg  of  the  horse,  in  the  wing  of 
the  bat,  and  in  the  flipper  of  the  seal,  are  of  special  use  to 
these  animals.  We  may  safely  attribute  these  structures  to 
inheritance.  But  to  the  progenitor  of  the  upland  goose  and 
of  the  frigate-bird,  webbed  feet  no  doubt  were  as  useful  as 
they  now  are  to  the  most  aquatic  of  living  birds.  So  we  ma^' 
believe  that  the  progenitor  of  the  seal  did  not  possess  a  flipper, 
but  a  foot  with  live  toes  fitted  for  walking  or  grasping;  and 
we  may  further  venture  to  believe  that  the  several  bones  in 
the  liml)s  of  the  monkey,  horse,  and  bat,  which  have  been  in- 
herited from  some  ancient  progenitor,  were  formerly  of  more 
special  use  than  they  now  are  to  these  animals  M'ith  their 
Avidely-diversificd  habits,  and  might  consequently  have  been 
modilied  through  natural  selection,  M:>king  due  allowance 
for  the  definite  action  of  changed  conditions,  correlation,  rever- 
sion, etc.,  we  may  conclude  that  every  detail  of  structure  in 
every  living  creature  is  either  now  or  was  formerly  of  use — 
directly  or  indirectly  through  the  comj^lex  laws  of  growth. 

With  respect  to  the  belief  that  organic  beings  have  been 
created  beautiful  for  the  delight  of  man — a  view  which  it  has 
been  pronounced  may  safely  be  accepted  as  true,  and  as  sub- 
versive of  my  whole  theory — I  may  first  remark  that  the  idea 
of  the  beauty  of  any  object  obviously  d(^pends  on  the  mind  of 
man,  irrespective  of  any  real  quality  in  the  a(hnircd  object ;  and 
that  the  idea  is  not  an  innate  and  imalterable  element  in  the 
mind.  We  see  this  in  men  of  ditlerent  races  admiring  an  en- 
tirely diirerent  standard  of  beauty  in  their  women  ;  neither  the 


Cii-vr.  VI.  BEAUTY    HOW  ACQUU4ED.  195 

Negro  nor  the  Chinese  admires  the  Caucasian  bcau-idcal.  The 
idea  also  of  picturesque  beauty  in  scenery  has  arisen  only  within 
modern  times.  On  the  view  of  beautiful  objects  havinj^  been 
created  for  man's  gratification,  it  ought  to  be  shown  that  there 
was  less  beauty  on  tlie  face  of  the  earth  before  man  appeared 
than  since  he  canae  on  the  stage.  Were  the  l^cautiful  volute 
and  cone  shells  of  the  Eocene  epoch,  and  the  gracefully-sculi> 
tured  ammonites  of  the  Secondary  period,  created  that  man 
might  ages  afterward  admire  them  in  his  cabinet  ?  Few  ob- 
jects are  more  beautiful  than  the  minute  siliceous  cases  of  the 
diatomacea? :  were  these  created  that  they  might  be  examined 
and  admired  xmder  the  higher  powers  of  the  microscope?  The 
beauty  in  this  latter  case,  and  in  many  others,  is  apparently 
wholly  due  to  symmetry  of  growth.  Flowers  rank  among  the 
most  beautiful  productions  of  Nature ;  and  they  have  become 
through  natural  selection  beautiful,  or  rather  conspicuous  in 
'contrast  with  the  green  leaves,  that  they  might  easily  be  ob- 
served and  visited  by  insects,  so  that  their  fertilization  miglit 
b'3  favored.  I  have  come  to  this  conclusion  from  finding  it  an 
invariable  rule  that  when  a  flower  is  fertilized  by  the  wind  it 
never  has  a  gayly-colored  corolla.  Again,  several  plants  habitu- 
ally produce  two  kinds  of  flowers  :  one  kind  open  and  colored 
so  as  to  attract  insects;  the  other  closed  and  iiot  colored,  desti- 
tute of  nectar,  and  never  \-isited  by  insects.  Hence  we  may 
conclude  that,  if  insects  had  never  existed  on  the  face  of  the 
earth,  the  vegetation  would  not  have  been  decked  Avith  beauti- 
ful flowers,  but  Avould  have  produced  only  such  poor  flowers  as 
we  now  see  on  our  firs,  oaks,  nut  and  ash  trees,  on  grasses, 
spinach,  docks,  and  nettles.  A  similar  line  of  argument  holds 
good  with  the  many  kinds  of  beautiful  fruits  ;  that  a  ripe  straw- 
berry or  cherry  is  as  pleasing  to  the  eye  as  to  the  palat<%  that  the 
gayly-colored  fruit  of  the  spindle-wood-tree  and  the  scarlet 
berries  of  the  holly  are  beautiful  objects,  will  be  admitted  by 
every  one.  But  this  beauty  serves  merely  as  a  guide  to  birds 
and  beasts,  that  the  fruit  may  be  devoured  and  the  manured 
seeds  thus  disscminatod  :  I  infer  that  this  is  the  case  from  havhig 
as  yet  found  in  every  instance  that  seeds,  Avhich  are  embedded 
within  a  fruit  of  any  king,  tliat  is  witliin  a  fleshy  or  pulpy  envel- 
ope, if  it  be  colored  of  any  brilliant  tint,  or  merely  rendered 
conspicuous  by  being  white  or  black,  are  always  disseminated 
by  being  first  devoured. 

On  the  other  hand,  I  willinglv  admit  that  a  great  nuinlKT 
of  male  animals,  as  all  our  ir.<  st  jrorgcous  birds,  some  f\^he3 


190  UTILITARIAN  DOCTRINE  HOW  FAR  TRUE:        Chap.  VI. 

some  maimnals,  and  a  host  of  majTnificently-colored  butterflies 
and  some  other  insects,  have  been  rendered  beautiful  for 
beauty's  sake ;  but  this  has  Ijcen  cfTected  not  for  the  dehf^ht 
of  man,  but  throup^'h  sexual  selection,  that  is,  from  the  more 
beautiful  males  liaving  been  continually  preferred  by  their  less 
ornamented  females.  So  it  is  Avith  the  music  of  birds.  We 
may  infer  from  all  this  that  a  similar  taste  for  lieautiful  colors 
ami  for  musical  sounds  runs  throug-h  a  large  part  of  the  animal 
kingilom.  AVhen  tlie  female  is  as  beautifully  colored  as  the 
male,  Avhich  is  not  rarely  the  case  with  birds  and  butterflies, 
the  cause  simply  lies  in  the  colors  acquired  throuo-h  sexual  se- 
lection having  been  transmitted  to  both  sexes,  instead  of  to 
the  males  alone.  In  some  instances,  however,  the  acquirement 
of  conspicuous  colors  by  the  female  may  have  been  checked 
through  natural  selection,  on  account  of  the  danger  to  which 
she  would  thus  have  been  exposed  during  incubation. 

Natural  selection  cannot  possibly  produce  any  modification 
in  any  one  species  exclusively  for  the  good  of  another  species ; 
though  throughout  Nature  one  species  incessantly  takes  advan- 
tage of,  and  profits  by,  the  structure  of  others.  But  natural 
selection  can  and  does  often  produce  structures  for  the  direct 
injury  of  otlicr  animals,  as  we  see  in  the  fang  of  the  adder,  and 
in  the  ovipositor  of  the  ichneumon,  by  which  its  eggs  are  depos- 
ited in  the  living  bodies  of  other  insects.  If  it  could  be  proved 
that  any  part  of  the  structure  of  any  one  species  had  been 
formed  for  the  exclusive  good  of  another  species,  it  would 
annihilate  my  theory,  for  such  could  not  have  been  produced 
through  natural  selection.  Although  many  statements  may 
be  found  in  Avorks  on  natural  history  to  tliis  eflcct,  I  cannot 
find  even  one  which  seems  to  me  of  any  weight.  It  is  admitted 
that  the  rattlesnake  has  a  poison-fang  for  its  own  defence  and 
for  the  destruction  of  its  prey ;  but  some  authors  supjiose  that 
at  the  same  time  this  snake  is  furnished  with  a  rattle  for  its 
own  injury,  namely,  to  warn  its  prey  to  escape.  I  would 
almost  as  soon  believe  that  the  cat  curls  the  end  of  its  tail 
wlicn  ])reparing  to  spring,  in  order  to  warn  the  doomed  mouse. 
But  I  have  not  space  here  to  enter  on  this  and  other  such  cases. 

Natural  selection  will  never  produce  in  a  being  any  thing 
injurious  to  itself,  for  natural  selection  acts  solely  by  and  for 
the  good  of  each.  No  organ  will  be  formed,  as  Palcy  has 
remarked,  for  the  purpose  of  causing  pain  or  fordoing  an  injury 
to  its  possessor.  If  a  fivir  balance  be  struck  between  the  good 
a-.id  evil  caused  by  each  part,  each  will  1w  found  on  the  whole 


Chap.  VI.  BE.VUTY   HOW  ACQUIKKD.  197 

advantagccous.  After  the  lapse  of  time,  under  changing  con- 
ditions of  life,  if  any  part  comes  to  be  injurious,  it  will  be  modi- 
fied; or,  if  it  be  not  so,  the  being  will  become  extinct,  as 
myriads  have  become  extinct. 

Natural  selection  tends  only  to  make  each  organic  being  as 
perfect  as,  or  sliglitly  more  perfect  than,  the  other  inliabitants 
of  the  same  country  with  which  it  has  to  struggle  for  existence. 
And  we  see  that  this  is  the  degree  of  perfection  attained  under 
nature.  Tlie  endemic  productions  of  New  Zealand,  for  instance, 
are  perfect  one  compared  with  another;  but  tlicy  are  now 
rapidly  yielding  before  the  advancing  legions  of  ])lants  and 
animals  introduced  from  Europe.  Natural  selection  will  nc»t 
produce  absolute  perfection,  nor  do  we  always  meet,  as  far  as 
we  can  judge,  with  tliis  high  standard  under  nature.  The  cor- 
rection for  the  al)erration  of  light  is  said  by  !Mliller  not  to  be 
perfect  even  in  that  most  perfect  organ,  the  human  eye.  If  our 
•reason  leads  us  to  admire  with  enthusiasm  a  multitude  of  in- 
imitable contrivances  in  nature,  this  same  reason  tells  us,  though 
we  may  easily  err  on  both  sides,  that  some  other  contrivances 
are  less  perfect.  Can  we  consider  the  sting  of  the  bee  as  per- 
fect, which,  when  used  against  many  attacking  animals,  cannot 
be  withdrawn,  owing  to  the  backward  scrratures,  and  so  inevi 
tably  causes  the  death  of  the  insect  by  tearing  out  its  viscera  ? 

if  we  look  at  the  sting  of  the  bee,  as  having  originally  ex- 
isted in  a  remote  progenitor  as  a  boring  and  serrated  instru- 
ment, like  that  in  so  many  members  of  the  same  great  order, 
and  wliich  has  been  modified  but  not  perfected  for  its  present 
purjiose,  with  the  poison  originally  adapted  for  some  other 
pur[)ose,  such  as  to  produce  galls,  subsequently  intensified,  mo 
can  ]ierhaps  understand  how  it  is  that  the  use  of  the  sting 
should  so  often  cause  the  insect's  own  death  :  for  if  on  the  whole 
the  power  of  stinging  be  useful  to  the  social  conununity,  it  will 
fulfil  all  the  requirements  of  natural  selection,  though  it  may 
cause  the  death  of  some  few  members.  If  we  admire  the  truly 
wonderful  power  of  scent  by  which  the  males  of  many  insects 
find  their  females,  can  we  admire  the  production  for  this  single 
purpose  of  thousands  of  drones,  which  are  utterly  useless  to  the 
community  for  any  other  purpose,  and  which  are  ultimately 
slaughtered  by  their  industrious  and  sterile  sisters  ?  It  may  be 
ditVicult,  Init  we  ought  to  admire  the  .savage  instinctive  hatred 
of  the  queen-bee,  which  urges  her  to  destroy  the  young  queens 
her  daughters  as  .soon  as  l)orn,  or  to  perish  herself  in  the  combat ; 
for  undoubtedly  this  is  for  the  good  of  the  community ;  and 


108  SUMMARY.  Cuap.  VI. 

inatcriKil  love  or  maternal  hatred,  though  the  latter  fortunately 
is  most  rare,  is  all  the  same  to  the  inexr)rablc  principle  of  natu- 
ral selection.  If  we  admire  the  several  ini^enious  contrivances, 
by  which  orchids  and  many  other  plants  are  fertilized  through 
insect  agency,  can  we  consider  as  equally  perfect  the  elabora- 
tion of  dense  clouds  of  pollen  by  our  fir-trees,  so  that  a  few 
granules  may  be  wafted  by  a  chance  breeze  on  to  the  ovules  ? 

Summary :  tJie  Law  of  Unity  of  Type  and  oftJie  Conditions 
of  Existence  embraced  by  the  Theory  of  JVcitural  Se- 
lection. 

We  have  in  this  chapter  discussed  some  of  the  difficulties 
and  objections  which  may  be  urged  against  the  theory.  Many 
of  them  are  serious  ;  but  I  think  that  in  the  discussion  light  has 
been  thrown  on  several  facts,  which  on  the  belief  of  indepen- 
dent acts  of  creation  are  uttercly  obscure.  We  have  seen  that 
species  at  any  one  period  are  not  indefinitely  variable,  and  are 
not  linked  together  by  a  multitude  of  intermediate  gradations, 
partly  because  the  process  of  natural  selection  will  always  be 
very  slow,  and  will  act,  at  any  one  time,  only  on  a  few  forms ; 
and  partly  because  the  very  process  of  natural  selection  implies 
the  continual  supplanting  and  extinction  of  preceding  and  in- 
termediate gradations.  Closely-allied  species,  now  living  on  a 
continuous  area,  must  often  have  been  formed  when  the  area 
was  not  continuous,  and  when  the  conditions  of  life  did  not  in- 
sensibly graduate  away  from  one  part  to  another.  When  two 
varieties  are  formed  in  two  districts  of  a  continuous  area,  an 
intermediate  variety  will  often  be  formed,  fitted  for  an  interme- 
diate zone  ;  but,  from  reasons  assigned,  the  intermediate  variety 
will  usually  exist  in  lesser  numbers  than  the  two  forms  which  it 
connects ;  consequently  the  two  latter,  during  the  course  of 
further  modification,  from  existing  in  greater  numbers,  Avill  have 
a  great  advantage  over  the  less  numerous  intermediate  variety, 
and  Avill  thus  generally  svicceed  in  sujiplanting  and  exterminat- 
ing it. 

AVe  have  seen  in  this  chapter  how  cautious  we  should  be 
in  concluding  that  the  most  different  habits  of  life  could  not 
graduate  into  each  other ;  that  a  bat,  for  instance,  could  not 
have  been  formed  by  natural  selection  from  an  animal  which 
at  first  could  only  glide  through  the  air. 

We  have  seen  that  a  species  may  under  new  conditions  of 
life  change  its  habits,  or  have  diversified  habits,  Avith  some  very 


Chap.  VI.  SUMMARY.  199 

unlike  those  of  its  ne:u-est  conveners.  Hence,  we  can  under- 
stand, bearing  in  mind  that  each  organic  being  is  trying  to  Hvc 
wliercver  it  can  live,  how  it  has  arisen  that  there  arc  upland 
geese  with  Avebbcd  feet,  ground  woodpeckers,  diving  thrushes, 
and  jx'trels  with  the  hal)its  of  auks. 

Although  the  belief  that  an  organ  so  perfect  as  the  eye 
could  have  been  formed  by  natural  selection,  is  more  than 
enouiih  to  sta^rger  any  one ;  yet  in  the  case  of  any  organ,  if  we 
know  of  a  long  series  of  gradations  m  complexity,  each  good 
for  its  possessor,  then,  under  changing  conditions  of  life,  there 
is  no  logical  impossibilit}'^  in  the  acquirement  of  any  conceivable 
degree  of  perfection  through  natural  selection.  In  the  cases 
in  which  we  know  of  no  intermediate  or  transitional  states,  we 
sliouhl  be  very  cautious  in  concluding  that  none  have  existed, 
for  the  homologies  of  man}'  organs  and  their  intermediate  states 
show  what  wonderful  metamorphoses  in  function  are  at  least 
'possible.  For  instance,  a  swim-bladder  has  apparently  been 
converted  into  an  air-breathing  lung.  The  same  organ  having 
performed  simultaneously  very  diflerent  functions,  and  then 
liaving  Ixicn  in  part  or  in  whole  specialized  for  one  function ; 
and  two  distinct  organs  having  performed  at  the  same  time  the 
same  function,  the  one  having  been  perfected  while  aided  by 
the  other,  must  often  have  largely-facilitated  transitions. 

We  have  seen  in  two  beings,  widely  remote  from  each  other 
in  the  natural  scale,  that  an  organ  serving  in  both  for  the  same 
purpose,  and  appearing  closely  similar,  may  have  been  sepa- 
rately and  independently  formed ;  but  when  such  organs  are 
closely  examined,  essential  dilTerences  in  their  structure  can 
almost  always  be  detected;  and  this  naturally  follows  from  the 
principle  of  natural  selection.  On  the  other  hand,  the  conunon 
rule  throughout  Nature  is  infinite  diversity  of  structure  for 
gaining  the  same  end;  and  this  again  naturally,  follows  on  the 
same  great  principle. 

In  almost  every  case  we  are  far  too  ignorant  to  be  enaljled 
lo  assert  that  any  part  or  organ  is  so  unimportant  for  the  wel- 
fare of  a  species,  that  modifications  in  its  structure  could  not 
have  been  slowly  accumulated  by  means  of  natural  selection. 
But  Ave  may  confidently  believe  that  many  modifications, 
wholly  due  to  the  laws  of  growth,  and  at  first  in  no  way  advanta- 
geous to  a  species,  have  been  subsef|uently  taken  advantage  of 
by  the  still  furtlier  modified  descendants  of  this  species.  We 
may  also  believe  tliat  a  part  formerly  of  high  importance  has 
often  been  retained  (as  tlie  tail  of  an  aquatic  animal  by  its  ter- 
restrial descendants),  though  it  has  become  of  such  small  im- 


200  SUMMAEY.  CiiAr.  VI. 

portancc  that  it  could  not,  in  its  present  state,  have  been  ac- 
quired by  natural  selection — a  power  which  acts  solely  through 
tlic  sur^-ival  of  tlie  best-fitted  individuals  in  the  strufrgle  for  life. 

Natural  selection  will  produce  nothing  in  one  sjiecies  foi 
the  exclusive  good  or  injury  of  anotlier;  though  it  may  well 
produce  parts,  organs,  and  excretions,  highly  useful  or  even  in- 
dispensable, or  highly  injurious  to  another  species,  but  in  all 
cases  at  the  same  time  useful  to  the  owner,  Natural  selection 
in  each  well-stocked  country  must  act  chiefly  through  the  com- 
pc^tition  of  the  inhabitants  one  with  another,  and  consequently 
will  produce  perfection,  or  strength  in  the  battle  for  life,  only 
according  to  the  standard  of  that  countrj^  Hence  the  inhab- 
itants of  one  countr}',  generally  the  smaller  one,  will  often  yield 
to  the  inhabitants  of  another  and  generally  larger  country.  For 
in  the  larger  country  there  will  have  existed  more  individuals, 
and  more  diversified  forms,  and  the  competition  will  have  been 
severer,  and  thus  the  standard  of  perfection  will  have  been 
rendered  higher.  Natural  selection  will  not  nccessarilj'  pro- 
duce absolute  perfection  ;  nor,  as  far  as  Ave  can  judge  by  our 
limited  faculties,  can  absolute  perfection  be  evei-ywhcrc  found. 

On  the  theory  of  natural  selection  we  can  clearly  inider- 
stand  the  full  meaning  of  that  old  canon  in  natural  history, 
"  Natura  non  facit  saltum."  This  canon,  if  we  look  only  to 
the  jiresent  inhabitants  of  the  world,  is  not  strictly  correct ; 
but  if  we  include  all  those  of  past  times,  whether  known  or 
not  yet  known,  it  must  by  my  theory  be  strictly  true. 

It  is  generally  acknowledged  that  all  organic  beings  have 
been  formed  on  two  groat  laws — Unity  of  Type,  and  the  Con- 
ditions of  Existence.  B}^  imity  of  type  is  meant  that  funda- 
mental agTcement  in  structure  which  we  see  in  organic  beings 
of  the  same  class,  and  which  is  quite  independent  of  their 
halnts  of  life.  .  On  my  theory,  unity  of  type  is  explained  by 
unity  of  descent.  The  expression  of  conditions  of  existence,  so 
often  insisted  on  by  the  illustrious  Cuvier,  is  fully  embraced  by 
tlie  principle  of  natural  selection.  For  natural  selection  acts 
by  either  now  adapting  the  varying  parts  of  each  being  to  its 
organic  and  inorganic  conditions  of  life  ;  or  by  having  adapted 
i\unn  during  long-past  periods  of  time  :  the  adaptations  being 
aided  in  some  cases  by  use  and  disuse,  being  affected  by  the 
direct  action  of  the  external  conditions  of  life,  and  being  in  all 
crises  subjected  to  the  several  laws  of  growth.  Hence,  in  fact, 
the  law  of  the  Conditions  of  Existence  is  the  higher  law  ;  as  it 
iiuhidcs,  thrnugli  the  inheritance  of  former  adaptations,  that 
of  Unity  of  Type, 


Cii.i.Vll.  INSTINCT.  201 


CHAPTER   VII. 

INSTINCT, 

Instincts  coniparnl)lo  with  Ilabiis,  but  difTcront  in  their  Orii^in— Inptincls  £;radu.ited 
— Aphides  and  Ants— Instincts  vnriable— DomcBtic  Instincts,  tlicir  Origin— Nat- 
ural luHtincta  of  tlic  Cuckoo.  Ostrich,  and  Parasitic  Bees— Slave-niakin:,'  Ants— 
Hive-bee,  its  cell-inakini;  instinct— Changes  of  Instinct  and  Structure  not  neces- 
sarily simultaneous- DilDculties  of  the  Theory  of  the  Natural  tjelectiou  of  lu- 
btincta— Neuter  or  Sterile  Insects — Summary. 

Instincts  might  have  been  worked  into  the  previous  chap- 
ters ;  but  I  thought  that  it  would  be  more  convenient  to  treat 
the  subject  separately,  especially  as  an  instinct  so  wonderful  as 
that  of  the  construction  of  the  comb  by  the  hive-bee  will  prob- 
ably have  occurred  to  many  readers,  :is  a  difficulty  sufficit-nt  to 
overthrow  the  whole  theory.  I  must  premise  that  I  have 
notliing  to  do  with  the  origin  of  tlic  primary  mental  powers, 
any  more  than  I  have  with  that  of  life  itself.  We  are  con- 
cerned only  with  the  diversities  of  instinct  and  of  the  other 
mental  qualities  of  animals  Avithin  the  same  class. 

I  will  not  attempt  any  definition  of  instinct.  It  would  be 
easy  to  show  that  several  distinct  mental  actions  are  commoidy 
embraced  by  this  term  ;  but  every  one  underst;uids  what  is 
meant,  when  it  is  said  that  instinct  impels  the  cuckoo  to  mi- 
grate and  to  lay  her  eggs  in  other  birds'  nests.  An  action, 
which  we  ourselves  should  require  experience  to  enable  us  to 
perform,  when  performed  by  an  animal,  more  especially  by  a 
very  young  one,  without  any  experience,  and  when  performed 
by  many  individuals  in  the  same  way,  without  their  knowing 
for  what  purpose  it  is  performed,  is  usutilly  said  to  he  instinc- 
tive. But  I  could  show  that  none  of  these  cliaracters  of  in- 
stinct are  universal.  A  little  dose,  as  Pierre  Hubcr  expresses 
it,  of  judgmtMit  or  rea.son,  often  comes  into  play,  even  in  ani- 
mals low  in  the  scale  of  nature. 

Frederick  Cuvier  and  several  of  the  older  m('tai)hysicians 
have  compared  instinct  with  habit.  This  comparLsou  gives,  I 
think,  an  accurate  notion  of  the  frame  of  mind  under  which 
an  instinctive  action  is  performed,  but  not  necessarily  of  its 


202  INSTINCT.  Chap.  VII. 

origin.  How  unconsciously  many  habitual  actions  are  per* 
fornieil,  indeed  not  rarely  in  direct  opposition  to  our  conscious 
Avill !  yet  tlicy  may  be  modified  by  the  ■will  or  reason.  Habits 
easily  become  associated  with  other  habits,  and  witli  certain 
periods  of  time  and  states  of  the  body.  A\'hcn  once  acquired, 
they  often  remain  constant  throughout  life.  Several  other  points 
of  resemblance  between  instincts  and  habits  could  be  pointed 
out.  As  in  repeating  a  well-known  song,  so  in  instincts,  one 
action  follows  another  by  a  sort  of  rhythm ;  if  a  ])erson  be  in- 
terrupted in  a  song,  or  in  repeating  any  thing  by  rote,  he  is 
generally  forced  to  go  back  to  recover  the  habitual  train  of 
thought :  so  P.  Huber  found  it  Avas  with  a  caterpillar,  which 
makes  a  very  complicated  hammock ;  for  if  he  took  a  cater- 
pillar which  had  completed  its  hammock  up  to,  say  the  sixth 
stage  of  construction,  and  put  it  into  a  hammock  completed  up 
only  to  the  third  stage,  the  caterpillar  simply  reperformed 
the  fourth,  fifth,  and  sixth  stages  of  construction.  If,  however, 
a  cater])illar  were  taken  out  of  a  hammock  made  up,  for  in- 
stance, to  the  third  stage,  and  were  put  into  one  finished  up  to 
the  sixth  stage,  so  that  much  of  its  work  was  already  done  for 
it,  far  from  feeling  the  benefit  of  this,  it  was  much  embarrassed, 
and,  in  order  to  complete  its  hammock,  seemed  forced  to  start 
from  the  third  stage,  where  it  had  left  off,  and  thus  tried  to 
complete  the  already-finished  work. 

If  we  suppose  any  habitual  action  to  become  inherited — and 
I  think  it  can  be  shown  that  tliis  does  sometimes  happen — 
then  the  resemblance  between  Avhat  originally  was  a  habit  and 
an  instinct  becomes  so  close  as  not  to  be  distinguished.  If 
Mozart,  instead  of  playing  the  jiiano-forte  at  three  years  old 
with  wonderfully  little  jiracticc,  had  played  a  tune  with  no 
l)ractice  at  all,  he  might  truly  be  said  to  have  done  so  instinc- 
tivclv.  But  it  would  be  a  serious  error  to  suppose  that  the 
greater  number  of  instincts  have  been  acquired  by  habit  in  one 
generation,  and  then  transmitted  by  inheritance  to  succeeding 
generations.  It  can  be  clearly  shown  that  the  most  wonder- 
ful instincts  with  which  we  arc  acquainted,  namely,  those  of 
the  hive-bee  and  of  many  ants,  could  not  possibly  have  been 
acqtiired  by  habit. 

It  will  be  universally  admitted  that  instincts  are  as  imjior- 
tant  as  corporeal  structure  for  the  welf:ire  of  each  species,  un- 
der its  present  conditions  of  life.  lender  changed  conditions 
of  life,  it  is  at  least  possible  that  slight  modifications  of  in- 
stinct might  be  profitable  to  a  species  ;  and  if  it  can  be  shown 


Chap.  VII.  INSTINCT.  203 

that  instincts  do  vary  ever  so  little,  then  I  can  see  no  dilTiculty 
in  natural  selection  preserving^  and  continually  accumulating 
variations  of  instinct  to  any  extent  that  was  profitable.  It  is 
thus,  as  I  believe,  that  all  the  most  complex  and  wonderful  in- 
stiijcts  have  originated.  As  modifications  of  corporeal  struct- 
ure arise  from,  and  arc  increased  b}'",  use  or  habit,  and  are 
diminished  or  lost  by  disuse,  so  I  do  not  doubt  it  has  been 
with  instincts.  But  I  believe  that  the  effects  of  habit  arc  of 
quite  subordinate  importance  to  the  effects  of  the  natural  selec- 
tion of  what  may  be  called  spontaneous  variations  of  instincts; 
tliat  is,  of  variations  produced  by  tlie  same  unknown  causes 
which  produce  slight  deviations  of  bodily  structure. 

No  comj^lex  instinct  can  possibly  be  produced  througli  nat- 
ural selection,  except  by  the  slow  and  gradual  accumulation 
of  numerous,  slight,  yet  profitable,  variations.  Hence,  as  in 
the  case  of  corporeal  structures,  we  ought  to  find  in  nature,  not 
the  actual  transitional  gradations  by  which  each  complex  in- 
stinct has  been  acquired — for  these  could  be  found  only  in  the 
lineal  ancestors  of  each  species — but  we  ought  to  find  in  the 
collateral  lines  of  descent  some  evidence  of  such  gradations  ; 
or  we  ought  at  least  to  be  able  to  shoAV  that  gradations  of 
some  kind  are  possible  ;  and  this  we  certainly  can  do.  I  have 
been  surprised  to  find,  making  allowance  for  the  instincts  of 
animals  having  been  but  little  observed  except  in  Europe  and 
North  America,  and  for  no  instinct  being-  kno^vn  among  extinct 
species,  how  very  generall^'^  gradations,  leading  to  the  most 
complex  instincts,  can  be  discovered.  Changes  of  instinct  may 
sometimes  be  facilitated  by  the  same  species  having  different 
instincts  at  different  periods  of  life,  or  at  different  seasons  of  the 
year,  or  when  placed  imder  difi'erent  circumstances,  etc.  ;  in 
which  case  cither  the  one  or  the  other  instinct  might  be  pre- 
served by  natural  selection.  And  such  instances  of  diversity 
of  instinct  in  the  same  species  can  be  shown  to  occur  in  nature. 

Again,  as  in  the  case  of  corporeal  structure,  and  conform- 
ably to  my  theorj-,  the  instinct  of  each  species  is  good  for  it- 
self, but  has  never,  as  far  as  we  can  judge,  been  produced  for 
the  exclusive  good  of  others.  One  of  the  strongest  instances 
of  an  animal  apparently  performing  an  action  for  the  sole  good 
of  another,  witli  which  I  am  acquainted,  is  that  of  ajihides  vol- 
untarily yielding,  as  was  first  observed  l)y  Hu})er,  their  sweet 
excretion  to  ants  ;  that  they  do  so  voluntarily,  the  following 
facts  show :  I  removed  all  the  ants  from  a  group  of  about  a 
dozen  aphides  on  a  dock-plant,  and  prevented  their  attendance 


204  INSTINCT.  CiiAr.  VII. 

during  several  hours.  After  this  interval,  I  felt  sure  that  the 
aphides  would  Avant  to  excrete.  I  watched  thcni  for  some 
time  through  a  lens,  but  not  one  excreted  ;  I  then  tickled  and 
stroked  them  with  a  hair  in  the  same  manner,  as  well  as  I 
could,  as  tlie  ants  do  with  their  antennre;  but  not  one  excreted. 
Afterward  I  allowed  an  ant  to  visit  them,  and  it  immediately 
seemed,  by  its  eager  way  of  running  about,  to  be  well  aware 
what  a  rich  Hock  it  had  discovered  ;  it  then  began  to  play  witli 
its  anteun;i3  on  the  abdomen  first  of  one  aphis  and  then  of  an- 
other; and  each,  as  soon  as  it  felt  the  antenna?,  immediately 
lifted  up  its  abdomen  and  excreted  a  limpid  drop  of  sweet 
juice,  which  was  eagerly  devoured  by  the  ant.  Even  the 
quite  young  aphides  behaved  in  this  manner,  showing  that  the 
action  Avas  instinctive,  and  not  the  result  of  experience.  It  is 
certain,  from  the  observations  of  Huber,  that  the  aphides  show 
no  dislike  to  the  ants  :  if  the  latter  be  not  present  they  are  at 
last  compelled  to  eject  their  excretion.  But  as  the  excretion 
is  extremely  viscid,  it  is  no  doubt  a  convenience  to  the  aphides 
to  have  it  removed ;  tlierefore,  probably  they  do  not  excrete 
solely  for  the  good  of  the  ants.  Although  there  is  no  evidence 
that  any  animal  performs  an  action  for  the  exclusive  good  of 
another  species,  yet  each  tries  to  take  advantage  of  the  in- 
stincts of  others,  as  each  takes  advantage  of  the  weaker  bodily 
structure  of  other  species.  So,  again,  certain  instincts  cannot 
be  considered  as  absolutely  perfect ;  but  as  details  on  this  and 
other  such  points  are  not  indispensable,  they  may  be  here 
passed  over. 

As  some  degree  of  variation  in  instincts  under  a  state  of 
nature,  and  the  inheritance  of  such  variations,  arc  indispensable 
for  the  action  of  natural  selection,  as  many  instances  as  pos- 
sible ought  to  be  here  given  ;  but  want  of  space  prevents  me. 
I  can  only  assert  that  instincts  certainly  do  vary — for  instance, 
the  migratory  instinct — both  in  extent  and  direction,  and  in  its 
total  loss.  So  it  is  with  the  nests  of  birds,  which  vary  partly 
in  dependence  on  the  situations  chosen,  and  on  the  nature  and 
temperature  of  the  country  inhabited,  but  often  from  causes 
Avliolly  unknown  to  us  :  Audubon  has  given  several  remarkable 
cases  of  differences  in  the  nests  of  the  same  species  in  the 
Northern  and  Southern  United  States.  A\''hy,  it  has  been  asked, 
if  instinct  be  variable,  has  it  not  granted  to  the  bee  "  the  ability 
to  use  some  other  material  Avhen  wax  was  deficient  ?  "  But 
what  other  material  could  bees  use?  They  Avill  work  with 
and  use,  as   I   have  seen,  wax   hardened  with  vermilion  and 


Chap.  VII.  CHANGES   OF  HABIT  OR  INSTINCT.  205 

softened"  with  lard.  Andrew  Knight  observed  that  his  bees, 
instead  of  laboriously  collecting  propolis,  used  a  cement  of 
wax  and  turpentine,  with  which  he  had  covered  decorticated 
trees.  It  has  lately  been  shown  that  bees,  instead  of  search- 
ing flowers  for  their  pollen,  will  gladly  use  a  very  different 
substance,  namely,  oatmeal.  Fear  of  any  particular  enemy  is 
certainly  an  instinctive  quality,  as  may  be  seen  in  nestling 
birds,  though  it  is  strengthened  by  experience,  and  by  the 
sight  of  fear  of  the  same  enemy  in  other  animals.  The  fear  of 
man  is  slowly  acquired,  as  I  have  elsewhere  shown,  by  the 
various  animals  which  inhabit  desert  islands ;  and  we  see  an 
instance  of  this  even  in  England,  in  the  greater  wildness  of 
all  our  large  birds  in  comparison  with  our  small  birds;  for 
llie  large  birds  have  been  most  persecuted  by  man.  '\\'e  may 
safely  attribute  the  greater  Avildness  of  our  large  birds  to  this 
cause  ;  for  in  iminhabited  islands  large  birds  are  not  more  fear- 
'ful  than  small ;  and  the  magjDie,  so  wary  in  England,  is  tame 
in  Norwa}',  as  is  the  hooded  crow  in  Egypt. 

That  the  mental  qualities  of  animals  of  the  same  kind, 
bom  in  a  state  of  nature,  vary  much,  could  be  shown  by 
many  facts.  Several  cases  could  also  be  given  of  occasional 
and  strange  habits  in  wild  animals,  which,  if  advantageous  to 
the  species,  might  give  rise,  through  natural  selection,  to 
new  instincts.  But  1  am  well  aware  that  these  general  state- 
ments, without  the  facts  in  detail,  Avill  produce  but  a  feeble 
effect  on  the  reader's  mind.  I  can  only  repeat  my  assurance, 
that  I  do  not  speak  without  good  evidence. 

Inherited  Chanr/cs  of  Ilah'it  or  Instinct  in  Domesticated  Animals. 

The  possibilit}',  or  even  probability,  of  inherited  varial  ions 
of  instinct  in  a  state  of  nature  Avill  be  strengthened  In'  briefly 
considering  a  few  cases  under  domestication.  Wc  shall  thus 
b(;  enabled  to  see  the  part  Avhich  habit  and  the  selection  of 
so-called  accidental  or  spontaneous  variations  have  plaj-ed  in 
modifying  the  mentiil  ([ualilies  of  our  domestic  animals.  It  is 
notorious  how  much  domestic  animals  vary  in  their  mental 
qualities.  With  cats,  for  instance,  one  naturally  takes  to  catch- 
ing rats,  and  another  mice,  and  these  tendencies  are  known 
to  be  inherited.  One  cat,  according  to  Mr.  St.  John,  alwavs 
brought  home  game-birds,  another  hares  or  rabbits,  and  another 
Inmtcd  on  marshy  ground  and  almost  nightly  caught  wood- 
cocks or  snipes.     A  number  of  curious  and  authentic  instancca 


20G  CHANGES  OF  HABIT   OR  INSTINCT  Chap.  VII. 

could  be  g'iven  of  various  shades  ol'  disjKjsitiou  and  of  taste, 
•  and  likcAvisc  of  the  oddest  tricks,  associated  with  certain  frames 
of  mind  or  periods  of  time,  being  inherited.  But  let  us 
look  to  the  familiar  case  of  the  breeds  of  the  dof^ :  it  cannot 
be  doubted  that  younj^  pointers  (I  have  myself  seen  a  striking 
instance)  "will  sometimes  point  and  even  back  other  dogs 
the  very  first  time  that  they  are  taken  out ;  retrie\-ing  is 
certainly  in  some  degree  inherited  by  retrievers ;  and  a  ten- 
dency to  run  round,  instead  of  at,  a  flock  of  sheep,  by  shep- 
herd-dogs. I  cannot  see  that  these  actions,  performed  with- 
out experience  by  the  young,  and  in  nearly  the  same  manner 
by  each  indi\'idual,  performed  with  eager  delight  by  each 
breed,  and  "without  the  end  being  known — for  the  young 
pointer  can  no  more  know  that  he  points  to  aid  his  master, 
than  the  white  butterfly  knows  why  she  lays  her  eggs  on 
the  leaf  of  the  cabbage — I  cannot  see  that  these  actions 
differ  essentially  from  true  instincts.  If  we  were  to  behold 
one  kind  of  wolf,  when  young  and  without  any  training,  as 
soon  as  it  scented  its  prey,  stand  motionless  like  a  statue, 
and  then  slowly  crawl  forward  with  a  peculiar  gait ;  and 
another  kind  of  wolf  rushing  round,  instead  of  at,  a  herd 
of  deer,  and  driving  them  to  a  distant  point,  we  should  assur- 
edly call  these  actions  instinctive.  Domestic  instincts,  as  they 
may  be  called,  are  certainly  far  less  fixed  than  natural  in- 
stincts; but  they  have  been  acted  on  by  far  less  rigorous  selec- 
lion,  and  have  been  transmitted  for  an  incomparably  shorter 
period,  imder  less  fixed  conditions  of  life. 

HoAV  strongly  these  domestic  instincts,  habits,  and  dis- 
positions, are  inherited,  and  how  curiously  they  become 
mingled,  is  well  shown  when  diflferent  breeds  of  dogs  are 
crossed.  Thus  it  is  known  that  a  cross  with  a  bull-dog  has 
afiFected  for  many  generations  the  courage  and  obstinacy  of 
greyhounds  ;  and  a  cross  Avith  a  greyhound  has  given  to  a 
whole  famih^  of  shepherd-dogs  a  tendency  to  hunt  hares. 
These  domestic  instincts,  when  thus  tested  by  crossing,  resem- 
ble natural  instincts,  which  in  a  like  manner  become  curiously 
blended  together,  and  for  a  long  period  exhibit  traces  of  the 
instincts  of  either  parent :  for  example,  Le  Koy  describes  a  dog, 
whose  great-grandfather  was  a  wolf,  and  this  dog  showed  a 
trace  of  its  wild  parentage  only  in  one  way,  by  not  com- 
ing in  a  straight  line  to  his  master,  when  called. 

Domestic  instmcts  are  sometimes  spoken  of  as  actions 
which    have    bec^.me    inherited   solelv    fi"om    long  -  continued 


CiiAP.  VII.  IN   DOMESTICATED   ANIMALS.  207 

and  compulsory  habit,  but  this  is  not  true.  No  one  would 
ever  have  thought  of  teaching,  or  probably  could  have 
taught,  the  tumbler-pigeon  to  tumble  —  an  action  which, 
as  I  have  witnessed,  is  performed  by  young  birds,  that 
have  never  seen  a  pigeon  tumble.  We  may  believe  that 
some  one  pigeon  showed  a  light  tendency  to  this  strange 
habit,  and  tlie  long-continued  selection  of  the  best  individ- 
uals in  successive  generations  made  tumblers  what  they  now 
are ;  and  near  Glasgow  there  are  house-tumblers,  as  I  hear 
from  Mr.  Brent,  which  cannot  fly  eighteen  inches  high  without 
going  head  over  heels.  It  may  be  doubted  whether  any 
one  would  have  thought  of  training  a  dog  to  point,  had  not 
some  one  dog  naturally  shown  a  tendency  in  this  line ;  and 
this  is  known  occasionally  to  happen,  as  I  once  saw,  in 
a  pure  terrier :  the  act  of  pointing  is  probably,  as  many 
have  thought,  only  the  exaggerated  pause  of  an  animal 
preparing  to  sjiring  on  its  prey.  When  the  first  tendency 
to  point  was  once  displayed,  methodical  selection  and  the 
inherited  effects  of  compulsory  training  in  each  successive 
generation  would  soon  complete  the  work  ;  and  unconscious 
selection  is  still  in  progress,  as  each  man  tries  to  procure, 
without  intending  to  improve  the  breed,  dogs  which  will 
stand  and  hunt  best.  On  the  other  hand,  habit  alone  in  some 
cases  has  sufficed  ;  hardly  any  animal  is  more  diflicult,  in  most 
cases,  to  tame  than  the  young  of  the  Avild  rabbit ;  scarcely  any 
animal  is  tamer  than  tlic  young  of  the  tame  rabbit;  bull 
can  hardly  suppose* that  domestic  rabbits  have  often  been 
selected  for  tameness  alone;  so  that  we  must  attribute  at 
least  the  greater  part  of  the  inherited  change  from  extreme 
wildness  to  extreme  tameness,  to  habit  and  long-continued 
close  confinement. 

Natural  instincts  are  lost  under  domestication  :  a  remark- 
able instance  of  this  is  seen  in  those  breeds  of  fowls  which 
very  rarely  or  never  become  "  broo<ly,"  that  is,  never  wish 
to  sit  on  tlieir  eggs.  Familiarity  alone  prevents  our  seeing 
how  largely  and  how  permanently  tlie  minds  of  our  domestic 
animals  have  been  modified.  It  is  scarcely  possible  to  doubt 
that  the  love  of  man  has  become  instinctive  in  tlie  dog. 
All  wolves,  foxe.s,  jackals,  and  species  of  the  cat  genus,  when 
kept  tame,  an;  most  eager  to  attack  poultry,  sheep,  and  pigs; 
and  this  tendency  has  been  found  incural)le  in  dogs  which 
liave  been  l)rought  home  as  jiuppies  from  coimtries,  such 
as  Tierra  del   Fuego  and   Australia,  where    the   savages    do 


208  SPECIAL  INSTINCTS.  Chap.  VII. 

not  keep  lliese  domestic  animals.  How  rarely,  on  the  other 
hand,  do  our  civilized  dogs,  even  when  quite  young,  require  to 
be  taught  not  to  attack  poultry,  sheep,  and  pigs  !  No  doubt 
they  occasionally  do  make  an  attack,  and  are  then  beaten ;  and 
if  not  cured,  they  are  destroyed ;  so  that  habit,  with  some  de- 
gree of  selection,  has  probably  concmred  in  civilizing  by  in- 
heritance our  dogs.  On  the  other  hand,  young  chickens 
have  lost,  wholly  by  habit,  that  fear  of  the  dog  and  cat 
which  no  doubt  was  originally  instinctive  in  them  •,  for  I 
am  informed  by  Captain  Hutton  that  the  young  chickens  of 
the  parent-stock,  the  Gallus  bankiva,  when  reared  in  India 
imder  a  hen,  are  at  first  excessively  wild.  So  it  is  with 
young  pheasants  reared  in  England  under  a  hen.  It  is  not 
that  chickens  have  lost  all  fear,  but  fear  only  of  dogs  and 
cats,  for  if  the  hen  gives  the  danger-chuckle,  they  will  nm 
(more  especially  young  turkeys)  from  under  her,  and  conceal 
themselves  in  the  surrounding  grass  or  thickets ;  and  this 
is  evidently  done  for  the  instinctive  purpose  of  allowing,  as 
we  see  in  wild  ground-birds,  their  mother  to  fly  away.  But 
tliis  instinct  retained  by  our  chickens  has  become  useless 
imder  domestication,  for  the  mother-hen  has  almost  lost  by 
disuse  the  power  of  flight. 

Hence,  we  may  conclude  that,  under  domestication,  in- 
stincts have  been  acquired,  and  natural  instincts  have  been 
lost,  partly  by  habit,  and  partly  by  man  selecting  and  accumu- 
lating, during  successive  generations,  peculiar  mental  habits 
and  actions,  which  at  first  appeared  from  what  we  must  in  our 
ignorance  call  an  accident.  In  some  cases  compulsory  habit 
alone  has  sufficed  to  produce  inherited  mental  changes ;  in 
othf^r  cases  compulsory  habit  has  done  nothing,  and  all  has 
been  the  result  of  selection,  pursued  both  methodically  and 
imconsciously :  but  in  most  cases  habit  and  selection  have 
probably  acted  together. 

Special  J/isti?ii't^'i. 

We  shall,  perhaps,  best  understand  how  instincts  in  a  slate 
of  nature  have  become  modified  by  selection,  by  considering  a 
few  cases.  I  will  select  only  three,  out  of  tliose  Avhich  I  sliall 
have  to  discuss  in  my  future  work — namely,  the  instinct  which 
leads  the  cuckoo  to  lay  her  eggs  in  other  birds'  nests :  the 
slave-making  instinct  of  certain  ants ;  and  the  cell-making 
power  of  the  hive-bee  :  these  two  latter  instincts  have  gcner- 


Chap.  VII.  INSTINCTS   OF  THE  CUCKOO.  209 

ally  and  justly  been  ranked  by  naturalists  as  the  most  wonder- 
ful of  all  known  instincts. 

Instincts  of  the  Cuckoo. — It  is  supposed  by  some  natu- 
ralists that  the  more  immediate  cause  of  the  instinct  of  the 
cuckoo  is  that  she  lays  her  ep^gs,  not  daily,  but  at  intervals  of 
two  or  three  days  ;  so  that,  if  she  were  to  make  her  own  nest 
and  sit  on  her  own  eg'p;s,  those  first  laid  would  have  to  be  left 
for  some  time  unincubatcd,  or  there  would  be  eggs  and  young 
birds  of  different  ages  in  tlie  same  nest.  If  this  Avere  the  case, 
tlie  process  of  laying  and  hatching  might  be  inconveniently 
long,  more  especially  as  she  migrates  at  a  very  early  period  ; 
and  the  first  hatched  young  would  prol:)abl3'  have  to  be  fed  by 
the  male  alone.  But  the  American  cuckoo  is  in  this  predica- 
ment ;  for  she  makes  her  own  nest,  and  has  eggs  and  young 
successively  hatched,  all  at  the  same  time.  It  has  been  both 
asserted  and  denied  that  the  American  cuckoo  occasionally 
lays  her  eggs  in  other  birds'  nests ;  but  I  have  lately  heard 
from  Dr.  Merrcll,  of  Iowa,  that  he  once  found  in  Illinois  a 
young  cuckoo  together  with  a  young  jay  in  the  nest  of  a  Blue 
jay  (Garrulus  cristatus)  ;  and  as  both  were  nearly  fully  feath- 
ered, there  could  be  no  mistake  in  their  identification.  I  could 
also  give  several  instances  of  various  birds  which  have  been 
known  occasionally  to  lay  their  eggs  in  other  birds'  nests. 
Now  let  us  suppose  that  the  ancient  progenitor  of  our  Euro- 
pean cuckoo  had  the  habits  of  the  American  cuckoo,  and  that 
she  occasionally  laid  an  e^^  in  another  bird's  nest.  If  the  old 
bird  profited  by  this  occasional  habit  through  being  enabled  to 
migrate  earlier  or  through  any  other  cause ;  or  if  the  yoimg 
were  made  more  vigorous  by  advantage  being  taken  of  the 
mistaken  instinct  of  another  species,  than  when  reared  by  their 
own  mother,  encumbered  as  she  could  hardly  fail  to  be  by 
having  eggs  and  young  of  different  ages  at  the  same  time ; 
then  the  old  birds  or  the  fostered  young  would  gain  an  advan- 
tage. And  analogy  would  lead  us  to  believe  that  the  young 
thus  roared  would  be  apt  to  follow  by  inheritance  the  occasion- 
al and  aberrant  habit  of  their  mother,  and  in  their  turn  would 
be  apt  to  lay  their  eggs  in  other  birds'  nests,  and  thus  be  more 
successful  in  rearing  their  young.  By  a  continued  process  of 
this  nature,  I  believe  that  the  strange  instinct  of  our  cuckoo 
has  been  generated.  It  has,  also,  recently  been  ascertained 
that  the  cuckoo  occasionally  lays  her  eggs  on  the  bare  ground, 
sits  on  them  and  feeds  her  young  ;  this  rare  and  strange  event 
evidently  is  a  case  of  reversion  to  the  long-lost  aboriginal  in- 
stinct of  nidification. 


210  SPECIAL  INSTINCTS.  Chap.  VII. 

It  has  been  objected  that  I  liave  not  noticed  other  related 
instincts  and  adaptations  in  the  cuckoo,  which  are  falsely 
spoken  of  as  necessarily  coordinated.  But  in  all  cases,  specu- 
lation on  an  instinct  known  only  in  a  single  species  is  useless, 
for  we  have  no  facts  to  guide  us.  Until  quite  recently  the  in- 
stincts of  the  European  and  of  the  non-parasitic  American 
cuckoo  alone  Avere  known ;  now,  owing  to  Mr.  E.  Ramsaj^'s 
observations,  we  know  something  about  three  Australian  spe- 
cies, which  lay  their  eggs  in  other  birds'  nests.  The  chief 
points  are  three :  first,  that  the  cuckoo,  with  rare  exceptions, 
lays  only  one  egg  in  a  nest,  so  that  the  large  and  voracious 
young  l)ird  may  receive  ample  food.  Secondly,  that  the  eggs 
are  of  remarkably  small  size,  not  exceeding  those  of  the  sky- 
lark— a  bird  about  one-fourth  as  large  as  the  cuckoo.  That 
the  small  size  of  the  egg  is  a  real  case  of  adaptation  we  may 
infer  from  the  fact  of  the  non-parasitic  American  cuckoo  laying 
full-sized  eggs.  Thirdl}"-,  that  the  young  cuckoo,  soon  after 
birth,  has  the  instinct,  the  strength,  and  a  properly-shaped 
back,  for  ejecting  its  foster-brothers,  which  then  perish  from 
cold  and  hunger.  This,  it  has  been  boldly  maintained,  is  a 
beneficent  arrangement,  in  order  that  the  young  cuckoo  may 
get  sufficient  food,  and  that  its  foster-brothers  may  perish  be- 
fore they  have  acquired  much  feeling. 

Turning  now  to  the  Australian  species  ;  though  these  birds 
generally  lay  only  one  egg  in  a  nest,  it  is  not  rare  to  find  two 
and  even  three  eggs  in  the  same  nest.  In  the  Bronze  cuckoo 
the  eggs  vary  greatly  in  size,  from  eight  to  ten  lines  in  length. 
Now  if  it  had  been  of  any  advantage  to  this  species  to  have 
laid  eggs  even  smaller  than  those  now  laid,  so  as  to  have 
deceived  certain  foster-parents,  or,  as  is  more  probable,  to  have 
been  hatched  within  a  shorter  period  (for  it  is  asserted  that 
tliere  is  a  relation  between  size  and  the  period  of  incubation), 
then  there  is  no  difficulty  in  believing  that  a  race  or  species 
might  have  been  formed  which  would  have  laid  smaller  and 
smaller  eggs  ;  for  these  would  have  been  more  safely  hatched 
and  reared.  ^Ir.  Ramsay  remarks  that  two  of  the  Australian 
cuckoos,  Avhen  they  lay  their  eggs  in  an  open  nest,  manifest  a 
decided  preference  for  nests  containing  eggs  similar  in  color  to 
their  own.  Tlie  Eurojiean  sjiecies  certainly  manifests  some 
tendency  toward  a  similar  instinct,  but  not  rarely  departs  from 
it,  as  is  shown  by  her  laying  her  dull  and  pale-colored  eggs  in 
the  nest  of  the  Hedge-Avarbler  with  bright  greenish-blue  eggs. 
Had   our   cuckoo  invariably  displaj-ed   the  above   instinct,  it 


Cii.vr.  VII.  INSTINCTS  OF  THE   CUCKOO.  oji 

would  assuredly  have  been  added  to  those  Mhich  it  is  assumed 
must  all  have  been  acquired  together.  The  eg-gs  of  the  Aus- 
tralian ]3ronze  cuckoo  vary,  according  to  Mr.  Ixanisay,  to  an 
extraordinary  degree  in  color;  so  that  in  this  respect,  as  well 
as  in  size,  natural  selection  assuredly  might  have  secured  and 
iixed  any  advantageous  variation. 

With  reference  to  the  young  European  cuckoo  ejecting  its 
foster-brothers — it  must  first  be  remarked  that  Mr.  Gould,  who 
has  paid  particular  attention  to  this  subject,  is  convinced  that 
the  belief  is  an  error :  he  asserts  that  the  young  foster-birds 
are  generally  ejected  during  the  first  three  days,  when  the 
yoimg  cuckoo  is  quite  powerless  ;  he  maintains  that  the  young 
cuckoo  exerts,  l)y  its  hunger-cries,  or  by  some  other  means, 
such  a  fascination  over  its  foster-parents,  that  it  alone  receives 
food,  so  that  the  others  are  starved  to  death,  and  are  then 
tljrown  out,  like  the  egg-shells  or  the  excrement,  by  the  old 
birds.  He  admits,  however,  that  the  3'^oung  cuckoo  Avheu 
giown  older  and  stronger  may  have  the  power,  and  perhaps  the 
instinct,  of  ejecting  its  foster-brothers,  if  they  hapj)en  to  escape 
starvation  during  the  first  few  days  after  birth.  Mr.  Ramsay 
has  arrived  at  the  same  conclusion  regarding  the  Australian 
species :  he  states  that  the  young  cuckoo  is  at  first  a  little 
helpless  fat  creature,  but,  "  as  it  grows  rapidly,  it  soon  fills  up 
the  greater  part  of  the  nest,  and  its  unfortunate  companions, 
either  smothered  by  its  weight,  or  starved  to  death  through  its 
greediness,  are  thrown  out  by  their  parents."  Nevertlieless 
there  is  so  much  evidence,  both  ancient  and  recent,  that  the 
young  Eurojican  cuckoo  does  eject  its  foster-brothers,  that  this 
can  hardly  be  doubted.  Now,  if  it  were  of  great  importance 
to  the  young  cuckoo  to  receive  as  much  food  as  possible  soon 
after  birth,  I  can  sec  no  special  difficulty  in  its  gradually 
acrjuiring,  during  successive  generations,  the  habit  (perhaps 
through  mere  unintentional  restlessness),  the  strength,  and  the 
structure,  best  fitted  for  ejecthig  its  foster-brothers;  for  those 
young  cuckoos  which  had  such  habits  and  structure  would  be 
the  best  fed  and  most  securely  reared.  I  can  sec  no  more 
difficulty  in  this,  than  in  young  birds  acquiring  the  instinct  and 
the  temporary  hard  tips  to  their  beaks  for  breaking  through 
their  own  shells  —  or  than  in  young  snakes  having  in  their 
upper  jaws,  as  Owen  has  remarked,  a  transitory  sharp  tooth 
for  cutting  through  the  tough  egg-shell.  For  if  each  part  is 
liable  to  individual  variations  at  any  age,  and  the  variations 
tend  to  be  inherited  at  a  corresponding  age  —  propositions 


212  SPECIAL  IXSTLNOTS.  Ciiai-.  VII. 

which  caiiiioL  be  disputed — then  the  instincts  and  structure  of 
the  youns-;'  could  be  slowly  modified  as  well  as  those  of  the 
adult;  antl  both  cases  must  stand  or  fidl  with  the  whole  theory 
of  natural  selection. 

The  occasional  habit  of  birds  laying  their  eggs  in  other 
birds'  nests,  either  of  the  same  or  of  distinct  species,  is  not 
very  uncommon  with  the  Gallinaceas ;  and  this  perhaps  explains 
the  origin  of  a  singular  instinct  in  the  nearest  allied  group, 
that  of  ostriches.  For  several  hen-ostriches  unite  and  lay  first 
a  few  eggs  in  one  nest  and  then  in  another;  and  these  arc 
hatched  by  the  males.  This  instinct  may  probably  be  accounted 
for  by  the  ftict  of  the  hens  lajang  a  large  number  of  eggs,  but, 
as  in  the  case  of  the  cuckoo,  at  intervals  of  two  or  three  days. 
The  instinct,  however,  of  the  American  ostrich  has  not  as  yet 
been  perfected ;  for  a  surprising  number  of  eggs  lie  strewed 
over  the  plains,  so  that  in  one  day's  hunting  I  picked  up  no 
less  than  twenty  lost  and  wasted  eggs. 

T\Iany  bees  are  parasitic,  and  regularly  lay  their  eggs  in  the 
nests  of  other  kinds  of  bees.  This  case  is  more  remarkable 
than  that  of  the  cuckoo ;  for  these  bees  have  not  only  had  their 
instincts  but  their  structure  modified  in  accordance  with  their 
parasitic  habits ;  for  they  do  not  possess  the  pollen-collecting 
apparatus  which  Avould  have  been  indispensable  if  they  had 
stored  food  for  tlieir  own  yoimg.  Some  species,  likewise,  of 
Sphegida)  (wasp-like  insects)  are  parasitic  in  the  same  manner 
on  other  species ;  and  M.  Fabre  has  lately  shown  good  reason 
for  believing  that,  although  the  Tachytes  nigra  generally  makes 
its  OAvn  burrow  and  stores  it  with  paralyzed  prey  for  its  own 
larv;e,  yet  that,  when  this  insect  finds  a  burrow  already  made 
and  stored  by  another  sphex,  it  takes  advantage  of  the  prize, 
and  becomes  for  the  occasion  parasitic.  In  this  case,  as  Avith 
the  supposed  case  of  the  cuckoo,  I  can  see  no  difficulty  in  nat- 
ural selection  making  an  occasional  habit  permanent,  if  of  ad- 
vantage to  the  species,  and  if  the  insect,  whose  nest  and  stored 
food  are  thus  feloniously  appropriated,  be  not  thus  extermi- 
nated. 

Slave-male  hip  Instinct. — This  remarkable  instinct  Avas  first 
discovered  in  the  Formica  (Polyerges)  rufesccns  by  Pien-o 
Huber,  a  better  oliserv-er  even  than  his  celebrated  father.  This 
ant  is  absolutely  dependent  on  its  slaves ;  Avithout  their  aid, 
the  species  Avould  certainly  become  extinct  in  a  single  year. 
The  males  and  fertile  females  do  no  Avork  of  any  kind,  and  the 
Avorkers  or  sterile  females,  though   most  energetic  and   coura- 


Chap.  VII.  SLAVE-MAKIXG  INSTINCT.  213 

{2:eous  in  capturinp^  slaves,  do  no  otlier  work.  They  are  inca- 
paljle  of  makiiii^  their  own  nests,  or  of  feeding  their  own  larv'a3. 
When  the  old  nest  is  found  inconvenient,  and  they  have  to 
migrate,  it  is  the  slaves  which  determine  the  migration,  and 
actually  carry  their  masters  in  their  jaws.  So  utterly  helpless 
are  the  masters,  that  when  Hubcr  shut  up  thirty  of  them  with- 
out a  slave,  but  with  plenty  of  the  food  Avhich  they  like  best, 
and  with  tlieir  own  larvie  and  pupa3  to  stimulate  them  to  work, 
they  did  nothing;  they  could  not  even  feed  themselves,  and 
many  perished  of  hunger.  Huber  then  introduced  a  single 
slave  (F.  fusca),  and  she  instantly  set  to  work,  fed  and  saved  the 
survivors  ;  made  some  cells  and  tended  the  larv.T,  and  put  all  to 
rights.  What  can  be  more  extraordinary  than  these  avcII- 
ascertaincd  facts  ?  If  we  had  not  known  of  any  other  slave- 
making  ant,  it  would  have  been  hopeless  to  speculate  how  So 
wonderful  an  instinct  could  have  been  perfected. 

Another  species,  Formica  sanguinea,  Avas  likewise  first  dis- 
covered by  P.  Huber  to  be  a  slave-making  ant.  This  species 
is  found  in  the  southern  parts  of  England,  and  its  habits  have 
been  attended  to  by  Mr.  F.  Smith,  of  the  British  Museum,  to 
whom  I  am  nnich  indebted  for  information  on  this  and  other 
subjects.  Although  fully  trusting  to  the  statements  of  Hulxu' 
and  Mr.  Smith,  I  tried  to  approach  the  subject  in  a  skeptical 
frame  of  mind,  as  any  one  may  well  be  excused  for  doubting 
the  truth  of  so  extraordinary  and  odious  an  instinct  as  that  (jf 
making  slaves.  Hence  I  will  give  the  observations  wliicli  I 
made,  in  some  little  detail.  I  oj^ened  fourteen  nests  of  F.  san- 
guinea, and  found  a  few  slaves  in  all.  Males  and  fertile  fe- 
males of  the  slave  sj)ecics  (F.  fusca)  are  found  only  in  their 
own  proper  communities,  and  have  never  been  observed  in  the 
nests  of  F.  sanguinea.  The  slaves  are  black  and  not  above 
half  the  size  of  their  red  masters,  so  that  the  contrast  in  their 
appearance  is  great.  W^hen  the  nest  is  slightly  disturbed,  the 
slaves  occasionally  come  out,  and  like  their  masters  are  much 
agitated  and  defend  the  nest ;  when  the  nest  is  much  dis- 
turbed, and  the  larva^  and  pup:c  are  exposed,  the  slaves  work 
energetically  together  with  their  masters  in  carrying  them 
away  to  a  place  of  safety.  Hence,  it  is  clear,  that  the  slaves 
feel  quite  at  home.  During  the  nujuths  of  June  and  July,  on 
three  successive  years,  I  have  watched  for  many  hours  several 
nests  in  Surrey  and  Sussex,  and  never  saw  a  slave  either  leave 
or  enter  a  nest.  As,  during  these  months,  the  slaves  are  very  few 
in  numljcr,  I  thought  that  they  might  behave  differently  wlien 


214  SPECIAL  INSTINCTS.  Chap.  VII. 

more  numerous  ;  but  Mr.  Smith  informs  me  that  he  has  watched 
the  nests  at  various  liours  during'  May,  June,  and  Aui^ust,  both 
in  Surrey  and  Hamjishire,  and  lias  never  seen  tlie  slaves, 
thougli  present  in  large  nundjers  in  August,  either  leave  or 
enter  the  nest.  Hence  he  considers  them  as  strictly  house- 
hold slaves.  The  masters,  on  the  other  hand,  maybe  constant- 
ly seen  bringing'  in  materials  for  the  nest,  and  food  of  all  kinds. 
During  the  ^-ear  18G0,  however,  in  the  month  of  July,  I  came 
across  a  community  with  an  unusually  large  stock  of  slaves, 
and  I  observed  a  few  slaves  mingled  with  their  masters  leaving 
the  nest,  and  marching  along  the  same  road  to  a  tall  Scotch-fir- 
tree,  twenty-five  yards  distant,  which  they  ascended  together, 
prol)ably  in  search  of  aphides  or  cocci.  According  to  Huber, 
who  had  ample  opportimitics  for  observation,  the  slaves  in 
Switzerland  habitually  Avork  with  their  masters  in  making  the 
nest,  and  they  alone  open  and  close  the  doors  in  the  morning 
and  evening;  and,  as  Pluber  expressly  states,  their  jmncipal 
office  is  to  search  for  aphides.  This  difference  in  the  usual 
habits  of  the  masters  and  slaves  in  the  two  coinitries  probably 
depends  merely  on  the  slaves  being  captured  in  greater  num- 
bers in  Switzerland  than  in  England. 

One  day  I  fortunately  witnessed  a  migration  of  F.  sanguinea 
from  one  nest  to  another,  and  it  Avas  a  most  interesting  spec- 
tacle to  behold  the  masters  carefully  carrying  their  slaves  in 
their  jaws  instead  of  being  carried  by  them,  as  in  the  case  of  F. 
rufescens.  Another  day  my  attention  was  struck  by  about  a 
score  of  the  slave-makers  haunting  the  same  spot,  and  evidently 
not  in  search  of  food ;  they  approached  and  were  vigorously 
repulsed  b}^  an  independent  community  of  the  slave-species 
(F.  fusca) ;  sometimes  as  many  as  tliree  of  these  ants  cUnging 
to  the  legs  of  the  slave-making  F.  sanguinea.  The  latter  ruth- 
lessly killed  their  small  opponents,  and  carried  their  dead 
bodies  as  food  to  their  nest,  twenty-nine  yards  distant ;  but 
they  were  prevented  from  getting  any  pupre  to  rear  as  slaves. 
I  then  dug  up  a  small  parcel  of  the  pupa?  of  F.  fusca  from 
another  nest,  and  put  them  down  on  a  bare  spot  near  the  place 
of  combat;  they  were  eagerly  seized  and  carried  off  by  the 
tyrants,  who  perhaps  fancied  that,  after  all,  tliC}'  had  been  vic- 
torious in  their  late  combat. 

At  the  same  time  I  laid  on  the  same  place  a  small  parcel 
of  the  ]nipre  of  another  species,  F.  flava,  with  a  few  of  these 
little  yellow  ants  still  clinging  to  the  fragments  of  their  nest. 
Tliis  species  is  sometimes,  though  rarely,  made  into  slaves,  as 


Chap.  VII.  SLAVE-MAKING  INSTINCT.  215 

has  been  described  by  Mr.  Smith.  Although  so  small  a  species, 
it  is  very  com'ageoiis,  and  I  have  seen  it  ferociously  attack  other 
ants.  In  one  instance  I  found  to  my  surprise  an  independent 
connnunity  of  F.  llava  under  a  stone  beneath  a  nest  of  the 
slave-making  F.  sanguinea ;  and  when  I  had  accidentally  dis- 
turbed both  n«'sts,  tlie  little  ants  attacked  their  big  neighbors 
with  surprising  courage.  Now  I  was  curious  to  ascertain  wheth- 
er F.  sanguinea  could  distinguish  the  pupae  of  F.  fusca,  which 
they  habitually  make  into  slaves,  from  those  of  the  little  and 
furious  F,  llava,  which  they  rarely  capture,  and  it  was  evident 
that  they  did  at  once  distinguish  them;  for  we  have  seen  that 
they  eagerly  and  instantly  seized  the  pupre  of  F.  fusca,  whereas 
they  were  much  terrified  when  they  came  across  the  pupa?,  or 
even  the  earth  from  the  nest,  of  F.  flava,  and  cjuickly  ran  away ; 
but  in  about  a  quarter  of  an  hour,  shortly  after  all  the  little 
yellow  ants  had  crawled  away,  they  took  heart  and  carried  off 
the  pupaj. 

One  evening  I  visited  another  community  of  F.  sanguinea, 
and  found  a  number  of  these  ants  returning  home  and  entering 
their  nests,  carrying  the  dead  bodies  of  F.  fusca  (showing  that 
it  was  not  a  migration)  and  numerous  pupa?.  I  traced  a  long 
file  of  ants  burdened  Avith  booty,  for  about  forty  yards,  back  to 
a  very  thick  clump  of  heath,  whence  I  saw  the  last  individual  of 
F.  sanguinea  emerge,  carrying  a  pupa ;  but  I  was  not  able  to 
find  the  desolated  nest  in  the  thick  heath.  The  nest,  h^wnver, 
must  have  been  close  at  hand,  for  two  or  three  individuals  of 
F.  fusca  were  rushing  al^out  in  the  greatest  agitation,  and  one 
was  perched  motionless  with  its  own  pupa  in  its  mouth  on  the 
top  of  a  spray  of  heath,  an  image  of  despair,  over  its  ravaged 
liome. 

Such  are  the  facts,  though  tliey  did  not  need  confirmation 
by  me,  in  regard  to  the  wonderful  instinct  of  making  slaves. 
Let  it  be  observed  what  a  contrast  the  instinctive  habits  of  F. 
sanguinea  jiresent  with  those  of  the  Continental  F.  rufescens. 
The  latter  does  not  build  its  own  nest,  does  not  determine  its 
own  migrations,  does  not  collect  food  for  itself  or  its  young, 
and  cannot  even  feed  itself:  it  is  absolutely  dependent  on  its 
numerous  slaves.  Formica  sanguinea,  on  the  other  hand,  pos- 
sesses much  fewer  slaves,  a!id  in  the  early  part  of  the  summer 
extremely  few  :  the  mastcTS  determine  when  and  where  a  new 
nest  shall  be  formed,  and,  when  they  migrate,  the  masters  carry 
the  slaves.  Both  in  Switzerland  and  England  the  slaves  seem 
to  have  the  exclusive  care  of  the  lurviu,  and  the  masters  alono 


•216  SPECLiL  INSTINCTS.  Chap.  VII. 

go  on  slave-making  expeditions.  In  Switzerland  the  slaves 
and  masters  Avork  together,  making  and  bringing  materials  for 
the  nest;  both,  l)iit  cliiefly  the  slaves,  tend,  and  milk,  as  it  may 
be  called,  their  aphides ;  and  thus  both  collect  food  for  the 
community.  In  England  the  masters  alone  usually  leave  the 
nest  to  collect  Ijuilding-materials  and  food  for  themselves,  their 
slaves  and  larva^.  So  that  the  masters  in  this  country  receive 
much  less  service  from  their  slaves  than  they  do  in  Switzerland. 

By  what  steps  the  instinct  of  F.  sanguinea  originated  I 
will  not  pretend  to  conjecture.  But  as  ants,  which  are  not 
slave-makers,  Avill,  as  I  have  seen,  carry  off  pupoe  of  other  spe- 
cies, if  scattered  near  their  nests,  it  is  possible  that  such  pupaj 
originally  stored  as  food  might  become  developed  ;  and  the 
foreign  ants  thus  unintentionally  reared  would  then  follow  their 
proper  instincts,  and  do  what  work  they  could.  If  their  pres- 
ence proved  useful  to  the  species  which  had  seized  them — if  it 
Avere  more  advantageous  to  tliis  species  to  capture  workers 
than  to  procreate  them — the  habit  of  collecting  pupa?  originally 
for  food  might  by  natural  selection  be  strengthened  and  ren- 
dered i^ermanent  for  the  very  different  purpose  of  raising  slaves. 
When  the  instinct  was  once  acquired,  if  carried  out  to  a  much 
less  extent  even  than  in  our  British  F.  sanguinea,  which,  as 
we  have  seen,  is  less  aided  by  its  slaves  tlian  the  same  species 
in  Switzerland,  natural  selection  might  increase  and  modify  the 
instinf"*^ — always  supposing  each  modification  to  be  of  use  to 
th(;  species — until  an  ant  Avas  fcn-med  as  abjectly  dependent  on 
its  slaves  as  is  the  Formica  rufcscens. 

Cell-making  Instinct  of  the  IIivc-J3ee. — I  will  not  here 
enter  on  minute  details  on  this  subject,  but  Avill  merely  give  an 
outline  of  the  conclusions  at  Avhich  I  have  arrived.  He  must 
be  a  dull  man  Avho  can  examine  the  exquisite  structure  of  a 
comb,  so  beautifully  adapted  to  its  end,  without  enthusiastic 
admiration.  We  hear  from  mathematicians  that  bees  have 
jiractically  solved  a  recondite  ]irobk'm,  and  have  made  their 
cells  of  the  proper  shape  to  hold  the  greatest  possible  amount 
of  hone}',  with  the  least  possible  consumption  of  precious  Avax 
in  their  construction.  It  has  been  remarked  that  a  skilful  Avork- 
man  Avith  fitting  tools  and  measures,  Avould  find  it  very  difficult 
to  make  cells  of  Avax  of  the  true  form,  though  this  is  jierfectly 
elTected  by  a  croAvd  of  bees  Avorking  in  a  dark  hive.  Granting 
whatever  instincts  you  please,  it  seems  at  first  quite  inconceiv- 
able how  they  can  make  all  the  necessary  angles  and  planes, 
or  even  perceive  Avhen  they  are  correctly  made.     But  the  dilli- 


OiiAP.  VII.  CELL-MAKING  INSTINCT.  217 

culty  is  not  nearly  so  great  as  it  at  first  appears  :  all  this  beau- 
tiful work  can  be  shown,  I  think,  to  follow  from  a  few  simple 
instincts. 

I  was  led  to  investigate  this  subject  by  INIr.  Waterhoiisc, 
who  hasshown  that  the  form  of  the  cell  stands  in  close  relation 
to  the  presence  of  adjoining  cells  ;  and  the  following  view  may, 
perhaps,  be  considered  only  as  a  modilicalion  of  his  theory : 
let  us  look  to  the  great  priucijile  of  gradation,  and  see  Avhether 
Nature  does  not  reveal  to  us  licr  method  of  woik.  At  one  end 
of  a  .short  series  we  have  huiuble-l)ees,  which  use  their  old 
cocoons  to  hold  honey,  soinctiTucs  adding  to  them  short  tubes 
of  wax,  and  liUewi.s<;  making  separate  and  very  iiTCgular  rounded 
cells  of  wax.  At  the  other  end  (if  the  series  Ave  have  the  cells 
of  the  hive-bee,  jilaced  in  a  doiil)le  la^-er:  each  cell,  as  is  well 
known,  is  an  hexagonal  prism,  with  the  basal  edges  of  its  six 
sides  bevelled  so  as  to  lit  on  to  a  pj-ramid,  formed  of  three 
rhombs.  These  rhombs  have  certain  angles,  and  the  three 
which  form  the  pyramidal  base  of  a  single  cell  on  one  side  of 
the  comb,  enter  into  the  composition  of  the  bases  of  three  ad- 
joining cells  on  the  opposite  side.  In  the  series  between  the 
extreme  perfection  of  the  cells  of  the  hive-bee  and  the  simpli- 
city of  those  of  the  humble-bee,  we  have  the  cells  of  the  Mexi- 
can ^lelipona  domestica,  carefully  described  and  figured  by 
Pierre  Iluber.  llie  I\Ielipona  itself  is  intermediate  in  structure 
between  the  hive  and  humble  bee,  but  more  nearly  related  to 
the  latter;  it  forms  a  nearly  regular  waxen  comb  of  cylindrical 
cells,  in  which  the  young  are  hatched,  and,  in  addition,  some 
large  cells  of  wax  for  holding  honey.  These  latter  cells  ai'e 
nearly  spherical  and  of  nearly  equal  sizes,  and  are  aggregated 
into  an  irregular  mass.  Ikit  the  important  point  to  notice  is, 
that  these  cells  are  always  made  at  that  degree  of  nearness  to 
each  other,  that  they  v>ould  have  intersected  or  broken  into 
each  other,  if  the  spheres  had  been  completed  ;  but  this  is  never 
permitted,  the  bees  building  pel-fectly  Hat  walls  of  wax  between 
the  spheres  which  thus  tend  to  intersect.  Hence  each  cell  con- 
sists of  an  outer  spherical  portion,  and  of  two,  three,  or  more 
perfectly  flat  surfaces,  according  as  the  cell  adjoins  two,  three, 
or  more  other  cells.  When  one  cell  rests  on  three  other  cells, 
which,  from  the  spheres  being  nearly  of  the  same  size,  is  very 
frequently  and  necessarily  the  case,  the  three  flat  surfaces  arc 
united  into  a  p}Tamid ;  and  this  pyramid,  as  Huber  has  re- 
marked, is  manifestlv  a  gross  imitation  of  the  three-sid(Ml  jiyram- 
'dal  baseji  of  th(>  cell  of  the  liivc'liee.  As  in  the  fells  of  the 
10 


218  SPECIAL  INSTINCTS.  Chap.  VII. 

hive-bee,  so  licre,  the  three  plane  surfaces  in  anyone  cell  neces- 
sarily enter  into  the  construction  of  three  adjoining  cells.  It 
is  obvious  that  the  Meli])ona  saves  wax,  and,  what  is  more  im- 
portant, lal)or,  by  this  manner  of  buildinjr;  for  the  Hat  walls 
between  the  adjoining  cells  are  not  double,  but  are  of  the  Siune 
thickness  as  the  outer  spherical  portions,  and  yet  each  flat  por- 
tion forms  a  part  of  two  cells. 

Rc^flecting  on  this  case,  it  occurred  to  me  that  if  the  Meli- 
pona  had  made  its  spheres  at  some  given  distance  from  each 
other,  and  had  made  them  of  erjnal  sizes,  and  had  arranged 
them  s^-nnnetrically  in  a  double  layer,  the  resulting  structure 
would  probably  have  been  as  perfect  as  the  comb  of  the  hive- 
bee.  Accordingly,  I  wrote  to  Prof.  Miller,  of  Cambridge,  and 
this  geometer  has  kindly  read  over  the  following  statement, 
drawn  up  from  his  information,  and  tells  me  that  it  is  strictly 
correct : 

If  a  number  of  equal  spheres  be  described  with  their  centres 
placed  in  two  parallel  layers,  with  the  centre  of  each  sphere  at 
the  distance  of  radius  X  1^  2,  or  radius  X  1.414:'21  (or  at  some 
lesser  distance),  from  the  centres  of  the  six  surrounding  spheres 
in  the  same  layer;  and  at  the  same  distance  from  the  centres 
of  the  adjoining  spheres  in  the  other  and  parallel  layer ;  then, 
if  planes  of  intersection  between  the  several  spheres  in  both 
layers  be  formed,  there  will  result  a  double  layer  of  hexagonal 
prisms  united  together  by  pyramidal  bases  formed  of  three 
rhombs ;  and  the  rhombs  and  the  sides  of  the  hexagonal  prisms 
will  have  every  angle  identically  the  same  with  the  best  meas- 
urements Avhich  have  been  made  of  the  cells  of  the  hive-bee. 
But  I  hear  from  Prof.  Wyman,  who  has  made  numerous  care- 
ful measurements,  that  the  accuracy  of  the  workmanship  of  the 
bee  has  been  greatly  exaggerated ;  so  much  so,  that,  as  he  adds, 
whatever  the  typical  form  of  the  cell  may  be,  it  is  rarely,  if 
ever,  realized. 

Hence,  we  may  safely  conclude  that,  if  Ave  could  slightly 
modify  the  instincts  already  possessed  by  the  Melipona,  and  in 
themselves  not  very  wonderful,  this  bee  would  make  a  structure 
as  wonderfully  perfect  as  that  of  the  hive-bee.  "We  must  sup- 
pose the  Melipona  to  have  the  power  of  forming  her  cells  truly 
spherical,  and  of  equal  sizes ;  and  this  would  not  be  very  sur- 
prising, seeing  that  she  already  does  so  to  a  certain  extent,  and 
seeing  what  perfectly  cvlindrical  burrows  in  wood  many  insects 
can  make,  apparently  by  turning  round  on  a  fixed  jioint.  AVc 
must  suppose  the  Melipona  (o  arrange  her  cells  in  level  layers, 


Chap.  VII.  CELL-MAKING  INSTINCT.  219 

as  she  already  does  her  cylindrical  cells ;  and  wc  uiiist  further 
suppose,  and  this  is  the  greatest  difliculty,  that  she  can  some- 
how judge  accurately  at  what  distance  to  stand  from  her  fellow- 
laborers  when  several  are  making  their  spheres;  but  she  is 
already  so  far  enabled  to  judge  of  distance,  that  she  alwa3-s 
describes  her  spheres  so  as  to  intersect  largely ;  and  then  she 
unites  tlie  points  of  intersection  by  perfectly  flat  surfaces. 
We  have  further  to  suppose,  but  this  is  no  difficulty,  that  after 
hexagonal  ])risnis  have  been  formed  by  the  intersection  of  ad- 
joining spheres  in  the  same  layer,  she  can  jirolong  the  hexagon 
to  any  length  requisite  to  hold  the  stock  of  hone}*;  in  the  same 
way  as  the  rude  humble-bee  adds  cylinders  of  wax  to  the  circu- 
lar mouths  of  her  old  cocoons,  ]5y  such  modifications  of  in- 
stincts, in  themselves  not  very  wonderful — hardly  more  wonder- 
ful than  those  which  guide  a  bird  to  make  its  nest — I  believe 
tluit  the  hive-bee  has  acquired,  through  natural  selection,  her 
inimitable  architectural  powers. 

But  this  theory  can  be  tested  by  experiment.  Following 
the  example  of  Mr.  Tegetmeier,  I  separated  two  combs,  and  put 
between  them  a  long,  thick,  rectangular  strip  of  wax  ;  the  bees 
instantly  began  to  excavate  minute  circular  pits  in  it ;  and  as 
they  deepened  these  little  pits,  they  made  them  wider  and 
wider  until  they  were  converted  into  shallow  basins,  appearing 
to  the  eye  jierfectly  true  or  parts  of  a  sphere,  and  of  about  the 
diameter  of  a  cell.  It  was  most  interesting  to  me  to  observe 
that, •wherever  several  bees  had  begun  to  excavate  these  basins 
near  together,  they  had  begun  their  work  at  such  a  distance  from 
each  other,  that  by  tlie  time  the  basins  had  acquired  the  above- 
stated  width  (i.  e.,  about  the  width  of  an  ordinary  cell),  and 
were  in  d<^pth  about  one-sixth  of  the  diameter  of  the  sphere  of 
M'hiih  they  formed  a  part,  the  rims  of  the  Ixisins  intersected  or 
broke  into  each  other.  As  soon  as  this  occurred,  the  bees 
ceased  to  excavate,  and  began  to  build  up  flat  walls  of  wax  on 
the  lines  of  intersection  between  the  basins,  so  that  each  hex- 
agonal prism  was  built  upon  the  scalloped  edge  of  a  smooth 
l)asin,  instead  of  on  the  straight  edges  of  a  three-sided  pyramid 
as  in  the  case  of  ordinary  cells. 

I  then  put  into  the  hive,  instead  of  a  thick,  rectangular 
\)\cce  of  wax,  a  thin  and  narrow,  knife-edged  ridge,  colored 
with  vermilion.  The  bees  instantlv  began  on  both  sides  to  ex- 
cavate little  basins  near  to  each  other,  in  the  same  way  as  be- 
fore; but  the  ridge  of  wax  was  so  thin,  that  the  bottoms  of  the 
basins,  if  they  had  been  excavated  to  the  same  depth  as  in  tlio 


220  SPECIAL  INSTINCTS.  Cuap.  VII. 

former  experiment,  would  liavc  broken  into  eacli  otlier  from 
the  opposite  sides.  The  bees,  liowcver,  did  not  sufl'er  this  to 
happen,  and  they  stopped  their  excavations  in  due  time ;  so 
that  the  basins,  as  soon  as  they  had  been  a  little  deepened, 
came  to  have  bottoms  with  flat  sides ;  and  these  flat  sides, 
formed  by  little  thin  plates  of  the  vermilion  wax  left  un- 
p^nawed,  were  situated,  as  far  as  the  eye  could  judge,  exactly 
along  the  planes  of  imaginary  intersection  between  the  basins 
on  tiie  opposite  sides  of  the  ridge  of  wax.  In  some  parts,  only 
small  portions,  in  other  parts,  large  portions  of  a  rhombic  jilate 
had  been  left  between  the  opposed  basins ;  but  the  work,  from 
the  mmatural  state  of  things,  had  not  been  neatly  performed. 
The  bees  must  have  worked  at  very  nearly  the  same  rate  in 
circularly  gnawing  away  and  deepening  the  basins  on  both 
sides  of  the  ridge  of  vennilion  wax,  in  order  to  have  thus  suc- 
ceeded in  leaving  flat  plates  between  the  basins,  by  stopping 
work  at  the  jilanes  of  intersection. 

Considering  how  flexible  thin  wax  is,  I  do  not  see  that 
there  is  any  dilficulty  in  the  bees,  while  at  work  on  the  two 
sides  of  a  strip  of  wax,  perceiving  when  they  have  gnawed  the 
wax  away  to  the  proper  thinness,  and  then  stopping  their  work. 
In  ordinarv  combs  it  has  appeared  to  me  that  the  bees  do  not 
always  succeed  in  working  at  exactly  the  same  rate  from  the 
opposite  sides ;  for  I  have  noticed  half-completed  rhombs  at 
the  base  of  a  just-commenced  cell,  which  were  slightly  concave 
on  one  side,  where  I  suppose  that  the  bees  had  excavated  too 
quickly,  and  convex  on  the  opposed  side  where  the  bees  had 
■worked  less  quickly.  In  one  well-marked  instance,  I  jiut  the 
coml)  back  into  the  hive,  and  allowed  the  bees  to  go  on  work- 
ing for  a  sliort  time,  and  again  examined  the  cell,  and  I  found 
that  the  rhombic  plate  had  been  completed,  and  had  become 
pcrfectli/  JJat :  i^  was  absolutely  impossil)le,  from  the  extreme 
thinness  of  the  little  plate,  that  they  could  have  effected  this 
by  gnawing  away  the  convex  side  ;  and  I  suspect  that  the  bees 
in  such  cases  stand  on  opposite  sides  and  push  and  bend  the 
ductile  and  warm  -wax  (which,  as  I  have  tried,  is  easily  done) 
into  its  ])roper  intermediate  plane,  and  thus  flatten  it. 

From  the  experiment  of  the  ridge  of  vermilion  wax  we  can 
Bee  that,  if  the  bees  were  to  build  for  themselves  a  thin  wall 
of  wax,  they  could  make  their  cells  of  the  proper  shape,  by 
standing  at  the  proper  distance  from  each  other,  by  excavat- 
ing at  the  same  rate,  and  by  endeavoring  to  make  equal  spheri- 
cal hollows,  but  never  allowing  the  s])hcres  to  break  into  each 


CuAP.  VII.  CELL-MAKING  INSTINCT.  221 

other.  Now  bees,  as  may  be  clearly  seen  hy  examining'  the 
od^e  of  a  ^rowinp^  comb,  do  make  a  roug'li,  circumferential 
^vall  or  rim  all  round  the  com)) ;  and  they  g'liaw  this  away  from 
the  op])()sitc  sides,  always  workinj]^  circularly  as  they  deepen 
each  cell.  They  do  not  make  the  whole  three-sided  pyramidal 
base  of  any  one  cell  at  the  same  time,  but  only  tliat  one  rhom- 
bic plate  Avhich  stands  on  the  extreme  growing  marg-in,  or  the 
two  plates,  as  the  case  may  be ;  and  th(>y  never  complete  the 
upper  edges  of  the  rhoml)ic  plates,  until  the  hexagonal  walls 
are  comnifmced.  Some  of  these  statements  dilTer  from  those 
made  by  the  justly-celebrated  elder  Uuber,  but  I  am  convinced 
of  their  accuracy  ;  and,  if  I  had  space,  I  could  show  that  they 
are  conformable  with  my  theory. 

Huber's  statement,  that  the  very  first  cell  is  excavated  ouJ 
of  a  little  parallel-sided  wall  of  wax,  is  not,  as  far  as  I  liavo 
seen,  strictly  correct ;  the  first  commencement  ha^'ing  always 
bben  a  little  hood  of  wax  ;  but  I  will  not  here  enter  on  these 
details.  We  see  how  important  a  part  excavation  plays  in  the 
construction  of  the  cells  ;  but  it  would  be  a  gn^at  error  to  sup- 
pose that  the  bees  cannot  l)uild  up  a  rough  Avail  of  M'ax  in  the 
proper  position — that  is,  along  the  plane  of  intersection  be- 
tween two  adjoining  si)heres.  I  have  several  specimens  show- 
ing clearly  that  they  can  do  this.  Even  in  the  rude  circum- 
ferential rim  or  wall  of  wax  round  a  growing  comb,  flexures 
may  sometimes  be  observed,  corresponding  in  position  to  the 
planes  of  the  rhombic  basal  plates  of  future  cells.  But  the 
rough  wall  of  wax  has  in  every  case  to  be  finished  ofl",  l)y  being 
largely  gnawed  away  on  both  sides.  The  manner  in  which 
the  bees  build  is  curious ;  they  always  make  the  first  rough 
wall  from  ten  to  twenty  times  thicker  than  the  excessively 
thin  finished  wall  of  the  cell,  which  will  ultimately  be  left. 
\\^o  shall  understand  how  they  work,  by  supposing  masons  first 
to  pile  up  a  broad  ridge  of  cement,  and  then  to  Ix^gin  cutting 
it  away  erjually  on  l)()th  sides  near  the  ground,  till  a  smooth, 
very  thin  wall  is  left  in  the  middle  ;  the  masons  always  piling 
up  the  cut-away  cement,  and  adding  fresh  cement  on  the  sum- 
mit of  tilt;  ridge.  "We  shall  thus  have  a  thin  wall  steadily 
growing  upward  but  always  crowned  by  a  gigantic  coping. 
From  all  tlu;  cells,  both  those  just  commenced  and  those  com- 
pleted, Ijcing  tluis  crowned  by  a  strong  coping  of  wax,  the 
bees  can  cluster  and  crawl  over  the  comb  without  injuring  the 
delicate  hexagonal  walls.  These  walls,  as  Prof.  Miller  has 
kindly  ascertained  for   me,  vary  greatly  in   thickness ;  being, 


222  SPECIAL  INSTINCTS.  Cuap.  VII. 

on  an  average  of  twelve  measurements  made  near  tlie  border 
of  tlic  comb,  Tp^  of  an  inch  in  thickness ;  whereas  the  basal 
rhomboidal  plates  are  thicker  nearly  in  the  proportion  of  three 
to  two,  having  a  mean  tliickness,  from  twenty-one  measure 
mcnts,  of  -rAs  of  an  inch,  liy  the  above  singular  maimer  of 
building,  strength  is  continually  given  to  the  coml),  with  the 
utmost  ultimate  economy  of  wax. 

It  seems  at  first  to  add  to  the  difficulty  of  understanding 
how  the  cells  are  made,  that  a  multitude  of  bees  all  work  to- 
gether ;  one  bee  after  Avorking  a  sliort  time  at  one  cell  going 
to  another,  so  that,  as  Hubcr  has  stated,  a  score  of  individuals 
work  even  at  the  commencement  of  the  first  cell.  I  was  able 
practicall}'"  to  show  this  fact,  by  covering  the  edges  of  tlie  hex- 
agonal walls  of  a  single  cell,  or  the  extreme  margin  of  the  cir- 
cumferential rim  of  a  growing  comb,  with  an  extremely  thin 
layer  of  melted  vermilion  wax  ;  and  I  invariably  found  that  the 
color  was  most  delicately  difiused  by  tlie  bees — as  delicately 
as  a  painter  could  have  done  with  his  brush — by  atoms  of  the 
colored  wax  having  been  taken  from  the  spot  on  which  it  had 
been  placed,  and  Avorked  into  the  growing  edges  of  the  cells 
all  round.  The  Avork  of  construction  seems  to  be  a  sort  of 
balance  struck  between  many  bees,  all  instinctively  standing 
at  the  same  relative  distance  from  each  other,  all  trying  to 
SAveep  equal  spheres,  and  tlien  building  up,  or  leaving  un- 
gnaAved,  the  planes  of  intersection  betAveen  these  spheres.  It 
was  really  curious  to  note  in  cases  of  difficulty,  as  Avhen  two 
pieces  of  comb  met  at  an  angle,  hoAV  often  the  bees  Avould  pull 
down  and  rebuild  in  different  ways  the  same  cell,  sometimes 
recurring  to  a  shaj^e  which  they  had  at  first  rejected. 

When  bees  haA'e  a  place  on  Avhich  they  can  starid  in  their 
proper  positions  for  Avorking — for  instance,  on  a  slip  of  Avood, 
placed  directly  under  the  middle  of  a  comb  groAving  doAvnAvard 
so  that  the  comb  has  to  be  built  OA'er  one  face  of  the  slip — in 
this  case  the  bees  can  lay  the  foundations  of  one  Avail  of  a  ncAV 
hexagon,  in  its  strictly  proper  place,  projecting  beyond  the 
other  com])leted  cells.  It  suffices  that  the  bees  should  be  en- 
al)led  to  stand  at  their  proper  relative  distances  from  each 
other  and  from  the  A\-alls  of  the  last  completed  cells,  and  then, 
by  striking  imaginary  spheres,  they  can  build  up  a  Avail  inter- 
mediate betAveen  tAvo  adjoining  s])heres ;  but,  as  far  as  I  have 
seen,  they  ncAxr  gnaw  aA\-ay  and  finish  off  the  angles  of  a  cell 
till  a  large  part  both  of  that  cell  and  of  the  adjoining  cells  has 
been  built.     This  capacity  in  bees  of  laying  doAvn  under  ccr- 


CiiAP.  VII.  rELL-MAKINO   INSTLXCT.  223 

tain  circumsluuccs  a  rough  wall  in  its  proper  place  l>elwccn  two 
just-commenced  cells,  is  important,  as  it  bears  on  a  fact,  which 
seems  at  first  quite  subversive  of  the  foregoing  theory ;  namely, 
that  the  cells  on  the  extreme  margin  of  Avasp-combs  are  some- 
times strictly  hexagonal ;  but  I  have  not  space  here  to  enter 
on  this  subject  Nor  does  there  seem  to  me  any  great  difii- 
culty  in  a  single  insect  (as  in  the  case  of  a  queen-wasp)  making 
hexagonal  cells,  if  she  were  to  work  alternately  on  the  inside 
and  outside  of  two  or  three  cells  commenced  at  the  same  time, 
always  standing  at  the  proper  relative  distance  from  the  parts 
of  the  cells  just  Ix^guji,  sweeping  spheres  or  cylinders,  and 
building  up  intermediate  planes. 

As  natural  selection  acts  only  by  the  accumulation  of  slight 
modificiitions  of  structure  or  instinct,  each  profitable  to  the 
individual  under  its  conditions  of  life,  it  may  reasonably  be 
asked,  how  a  long  and  graduated  succession  of  motlified  archi- 
tectural instincts,  all  tending  toward  the  prcsent  perfect  plan 
of  construction,  could  have  profited  the  progenitoi-s  of  the  hive- 
bee  ?  I  think  the  answer  is  not  diflicult:  cells  constructed 
like  those  of  the  bee  or  the  wasp  gain  in  strength,  and  save 
much  in  labor  and  space,  and  in  the  materials  of  which  they 
are  constructed.  With  respect  to  the  formation  of  wax,  it  is 
known  that  bees  are  often  hard  pressed  to  get  sufficient  nectar, 
and  I  am  informed  by  Mr.  Tegetmeier  that  it  has  been  experi- 
mentally proved  that  from  twelve  to  fifteen  poimds  of  dry 
sugar  arc  consumed  by  a  liive  of  bees  for  the  secretion  of  each 
pound  of  wax;  so  that  a  prodigious  quantity  of  fluid  nectar 
nmst  be  collected  and  consumed  by  the  bees  in  a  hive  for  the 
secretion  of  the  wax  necessary  for  the  construction  of  their 
combs.  Moreover,  many  bees  have  to  remain  idle  for  many 
days  during  the  jirocess  of  secretion.  A  large  store  of  honey 
is  indispensable  to  support  a  largt;  stock  of  bees  during  the 
winter ;  and  the  security  of  the  hive  is  known  mainly  to  depend 
on  a  large  number  of  bees  being  supported.  Hence  the  saving 
of  wax  by  largely  saving  honey  and  the  time  consumed  in  col- 
lecting the  honey  must  be  an  important  element  of  success  to 
any  family  of  bees.  Of  course,  the  success  of  the  species  ma\- 
be  dependent  on  the  number  of  its  enemies,  or  parasites,  or  on 
(juite  distinct  caiuses,  and  so  be  altogether  independent  of  the 
quantity  of  honey  which  the  bees  could  collect.  But  let  us 
suppose  that  this  latter  circumstance  determined,  as  it  proba- 
bly often  has  determined,  whether  a  bee  allied  to  our  liumble- 
bces  could  exist  in  large  nuinbere  in  any  country  ;  and  let  us 


224  SPECIAL  INSTINCTS.  Chap.  VII, 

further  suppose  lliat  tlie  community  lived  tlirou;^h  the  winter, 
and  consequently  required  a  store  of  honey;  there  can  in  this 
case  be  no  doubt  that  it  would  be  an  advantage  to  our  imagi- 
nary humble-bee,  if  a  slight  modification  in  her  instincts  led 
her  to  make  her  waxen  cells  near  together,  so  as  to  intci*sect  ;•- 
little ;  for  a  wall  in  common  even  to  two  adjoining  cells  would 
save  some  little  labor  and  wax.  Hence  it  would  continually 
be  more  and  more  advantageous  to  our  humble-bees,  if  they 
were  to  make  their  cells  more  and  more  regular,  nearer  to- 
gether, and  aggregated  into  a  mass,  like  the  cells  of  the  Jleli- 
])ona ;  for  in  this  case  a  large  part  of  the  bounding  surface  of 
each  cell  would  serve  to  bound  the  adjoining  cells,  and  much 
labor  and  wax  Avould  bo  saved.  Again,  from  the  same  cause, 
it  Avould  be  advantageous  to  the  Melipona,  if  she  were  to 
make  her  cells  closer  together,  and  more  regular  in  every  way 
than  at  present ;  for  then,  as  we  have  seen,  the  sjiherical  sm- 
faces  would  wholly  disappear  and  be  replaced  by  plane  sur- 
faces ;  and  the  Melipona  Avould  make  a  comb  as  perfect  as  that 
of  the  hive-bee.  Beyond  this  stage  of  perfection  in  architect- 
ure, natural  selection  could  not  lead ;  for  the  comb  of  the  hive- 
bee,  as  far  as  we  can  see,  is  absolutely  perfect  in  economizing 
labor  and  wax. 

Thus,  as  I  believe,  the  most  v.'onderful  of  all  known  in- 
stincts, that  of  the  hive-bee,  can  be  explained  by  natural  selec- 
tion having  taken  advantsige  of  numerous,  successive,  sUght 
modifications  of  simpler  instincts;  natural  selection  having,  by 
slow  degrees,  more  and  more  perfectly  led  the  bees  to  sweej) 
etjual  spheres  at  a  given  distance  from  each  other  in  a  double 
layer,  and  to  build  up  and  excavate  the  wax  along  the  planes 
of  intersection ;  the  bees,  of  course,  no  more  knowing  that 
they  swept  their  spheres  at  one  particular  distance  from  each 
other,  than  they  know  what  are  the  several  angles  of  the 
hexagonal  prisms  and  of  tlie  basal  rhombic  plates ;  the  motive 
jiower  of  tlie  process  of  natural  selection  having  been  the  con- 
struction of  cells  of  due  strength  and  of  the  proper  size  and 
shape  for  tlie  larv.o?,  this  being  etlected  Avith  the  greatest  pos- 
sible economy  of  labor  and  Avax  ;  that  individual  swarm  which 
thus  made  tlie  best  cells  with  least  lalior,  and  least  waste  of 
honey  in  tlie  secretion  of  wax,  having  succeeded  best,  and  liav- 
ing  transmitted  by  inheritance  their  newly-acquired  economical 
instincts  to  new  swarms,  which  in  their  turn  will  have  had  tho 
best  chance  of  succeeding  in  the  struggle  for  existence. 


CiiAi-.  VII.      OBJECTIONS   TO  NATDKAL  SELECTION.  225 

Objectiojis  to  the  Tlicory  of  Natural  Selection  as  cq^plied  to 
Instincts  y'  Axuter  and  Sterile  Insects. 

It  has  been  objected  to  the  foregoing  view  of  the  origin  of 
instincts  that  "  the  variations  of  structure  and  of  instinct  must 
have  been  simultaneous  and  accurately  adjusted  to  each  other, 
as  a  modification  in  the  one  without  an  immediate  corre- 
sponding change  in  the  other  Avould  have  been  fatal."  The 
force  of  this  olijection  rests  entirely  on  the  assumption  that  the 
changes  in  both  instinct  and  structure  are  abrupt.  To  take  as 
an  illustration  the  case  of  the  larger  titmouse  (Parus  major)  al- 
luded to  in  the  last  chapter :  this  l)ird  often  holds  the  seeds  of 
the  yew  between  its  feet  on  a  branch,  and  hannners  away  till 
it  gets  into  the  kernel.  Now  what  special  diiliculty  would 
there  be  in  natural  selection  preserving  all  the  slight  individ- 
ual variations  in  the  shape  of  the  beak,  Avhich  were  better  and 
better  adapted  to  break  ojien  the  seeds,  until  a  beak  was 
formed,  as  well  constructed  for  this  purpose  as  that  of  the  nut- 
hatch, at  the  same  time  that  habit,  or  compulsion,  or  sponta- 
neous variations  of  taste,  led  the  bird  to  become  more  and  more 
of  a  seed-eater  ?  In  this  case  the  beak  is  supposed  to  be  slowly 
modified  by  natural  selection,  subsequently  to,  but  in  accordance 
with,  slowly-changing  habits  or  taste ;  but  let  the  feet  of  the 
titmouse  vary  and  grow  larger  from  correlation  with  tlie  beak, 
or  from  any  other  imknown  cause,  and  it  is  not  improbable 
that  such  larger  feet  would  lead  the  bird  to  climb  more  and 
more  until  it  acquired  the  remarkable  climbing  instinct  and 
jwwer  of  the  nuthatch.  In  this  case  a  gradual  change  of  struct- 
ure is  supposed  to  lead  to  changed  instinctive  habits.  To 
take  one  more  case  :  few  instincts  are  more  remarkable  than 
that  which  leads  the  swift  of  the  Eastern  Islands  to  make  its 
nest  wholly  of  inspissated  saliva.  iSoine  birds  build  their  nests 
of  nnid,  believed  to  be  moistened  with  saliva  ;  and  one  of  the 
swifts  of  North  America  makes  its  nest  (as  I  have  seen)  of 
sticks  agglutinated  with  saliva,  and  even  with  flakes  of  this 
substance.  Is  it,  then,  very  improbable  that  the  natural  selec- 
tion of  individual  swifts,  wliich  secreted  more  and  more  saliva, 
should  at  last  produce  a  species  with  instincts  leading  it  to 
neglect  other  matc^rials^  and  to  make  its  nest  exclusively  of 
inspissated  saliva?  And  so  in  other  cases.  It  must,  however, 
be  admitted  tliat  in  many  instances  we  cannot  conjecture 
whetlier  it  was  instinct  or  structure  which  first  varied. 

No  doubt  many  instincts  of  very  dillicult  explanation  could 


226  OBJECTIONS   TO   THE   THEOICY  CriAP.  VII. 

be  0])poscJ  to  tlic  theory  of  natunil  selection — cases,  in  -which 
Ave  cannot  sec  how  an  instinct  could  ])ossibly  liave  originated; 
cases,  in  ■which  no  intermediate  gradations  arc  known  to  exist ; 
cases  of  instinct  of  such  trifling  importance,  that  they  could 
hardly  have  been  acted  on  by  natural  selection ;  cases  of  in- 
stincts almost  identically  the  same  in  animals  so  remote  in  the 
scale  of  Nature,  that  we  cannot  account  for  their  similarity  by 
inheritance  from  a  common  progenitor,  and  consequently  must 
believe  that  they  were  independently  acciuircd  through  natural 
selection.  I  will  not  here  enter  on  these  several  cases,  but 
will  confine  myself  to  one  special  difficulty,  which  at  first  ap- 
jieared  to  me  insuperable,  and  actuall}'  fatal  to  the  whole 
theory.  I  allude  to  the  neuters  or  sterile  females  in  insect- 
communities  :  for  these  neuters  often  differ  widely  in  instinct 
and  in  structure  from  both  the  males  and  fertile  females,  and 
yet,  from  being  sterile,  they  cannot  propagate  their  kind. 

The  subject  well  deserves  to  be  discussed  at  great  length, 
but  I  Avill  here  take  only  a  single  case,  that  of  working  or 
sterile  ants.  Hoav  the  workers  have  been  rendered  sterile  is  a 
difriculty  :  but  not  much  greater  than  that  of  any  other  strik- 
ing modification  of  structure  ;  for  it  can  be  shown  that  some 
insects  and  other  articulate  animals  in  a  state  of  nature  occa- 
sionally become  sterile ;  and  if  such  insects  had  been  social, 
and  it  had  been  profitable  to  the  community  that  a  numl^er 
should  have  been  annually  born  capable  of  work,  but  incapable 
of  procreation,  I  can  see  no  especial  difficulty  in  this  having 
been  efT(M'ted  through  natural  selection.  But  I  must  pass  over 
this  preliminary  difficulty.  The  great  difiiculty  lies  in  the 
working  ants  differing  widely  from  both  the  males  and  the 
fertile  females  in  structure,  as  in  the  shape  of  the  thorax,  and 
in  being  destitute  of  wings  and  sometimes  of  eyes,  and  in  in- 
stinct. As  far  as  instinct  alone  is  concerned,  the  Avonderful 
difference  in  this  respect  between  the  Avorkers  and  the  perfect 
females,  would  have  been  better  exemplified  by  the  hive-bee. 
If  a  working  ant  or  other  neuter  insect  had  been  an  ordinary 
animal,  1  should  have  mihesitatingly  assumed  that  all  its  char- 
acters had  been  slowly  acquired  through  natural  selection ; 
namely,  by  individuals  having  been  born  with  slight  profitable 
modifications,  which  were  inherited  by -the  offspring;  and  that 
these  again  varied  and  again  were  selected,  and  so  onward. 
But  with  the  Avorking  ant  we  have  an  insect  differing  greatly 
from  its  parents,  yet.  absolutely  sterile ;  so  that  it  could  never 
have  transmitted  successively-acquired  modifications  of  struct- 


Chap.  VII.  OF  NATURAL  SELECTION.  227 

lire  or  instinct  to  its  proc^ony.  It  may  well  be  asked  how  is 
it  possible  to  reconcile  this  case  with  the  theory  of  natural 
selection  ? 

First,  let  it  be  remembered  that  wc  have  innumeral)le  in- 
stances, both  in  our  domestic  productions  and  in  those  in  a 
state  of  nature,  of  all  sorts  of  differences  of  inherited  structure 
which  are  correlated  with  certain  ages,  and  with  either  sex. 
We  have  differences  correlated  not  only  Avith  one  sex,  but 
with  that  short  period  when  the  reproductive  system  is  active, 
as  in  the  nuptial  plumage  of  many  birds,  and  in  the  hooked 
jaws  of  the  male  salmon.  We  have  even  slight  differences  in 
the  horns  of  diQ'erent  breeds  of  cattle  in  relation  to  an  artifi- 
cially imperfect  state  of  the  male  sex ;  for  oxen  of  certain 
breeds  have  longer  horns  than  tlie  oxen  of  other  breeds,  rela- 
tively to  the  h'ugth  of  the  horns  in  both  the  bulls  and  cows  of 
these  same  breeds.  Hence  I  can  see  no  great  difficulty  in  any 
character  becoming  correlated  with  the  sterile  condition  of 
certain  members  of  insect  communities :  the  difficulty  lies  in 
understanding  how  such  correlated  modifications  of  structure 
could  have  been  slowly  accumulated  by  natural  selection. 

Tliis  dilficulty,  though  ajipearing  insuperable,  is  lessened, 
'  or,  as  I  believe,  disajjpears,  when  it  is  remembered  that  selec- 
tion may  l)e  applied  to  the  family,  as  well  as  to  the  individual, 
and  may  thus  gain  the  desired  end.  Thus,  breeders  of  cattle 
wish  the  flesh  and  fat  to  be  well  marbled  together ;  the  animal 
has  been  slaughtered,  but  the  breeder  has  gone  witli  confidence 
to  the  same  stock  and  has  succeeded.  Such  faith  may  be 
placed  in  the  power  of  selection,  that  probably  a  breed  of 
cattle,  always  yielding  oxen  Avith  extraordinarily  long  horns, 
could  be  slowly  formed  by  carefully  Avatching  Avhich  individual 
bulls  and  cows,  Avhen  matched,  produced  oxen  Avith  the  longest 
horns ;  and  yet  no  one  ox  Avould  ever  have  propagated  its 
kind.  Here  is  a  better  and  real  illustration  :  according  to  M. 
Vcrlot,  some  varieties  of  the  double  annual  stock  of  various 
colors,  from  having  been  long  carefully  selected  to  the  right 
degree,  always  produce  by  seed  a  large  projinrtion  of  plants 
l)earing  double  andf|nite  sterile  floAvers ;  so  that,  if  the  A'ariety 
had  not  likewise  yielded  others,  it  Avould  at  once  have  become 
extinct;  but  it  always  yields  some  single  and  fertile  plants, 
Avhich  differ  from  ordinary  single  A'arieties  only  in  their  power 
of  producing  the  two  forms.  Thus  the  fertile  plants  producing 
single  flowers  may  be  compared  Avith  the  males  and  females  of 
an  ant-comnumity,  and  the  sterile  double-flowered  plants,  Aviiich 


228  OBJECTIONS   TO  THE   THEOKY  Chap.  VII. 

arc  rcg'ularly  produced  in  l:ir^e  numbers,  with  tlu;  iiKiny  st4?rilo 
neuters  of  the  same  coininunity.  Thus  I  l>elieve  it  has  been 
"vvith  social  insects  :  a  slij^ht  modification  of  structure,  or  of  in- 
stinct, correlated  with  tlic  sterile  condition  of  certain  members 
of  the  conmiunity,  has  been  advantageous  to  the  community: 
consequently  the  fertile  males  and  females  of  tlie  same  cona- 
munity  flourished,  and  transmitted  to  their  fertile  ofl'sprinfr^  a 
tendency  to  produce  sterile  members  having  the  same  modifi- 
cation. And  I  believe  that  this  process  has  been  repeated, 
luitil  that  prodigious  amount  of  difference  between  the  fertile 
and  sterile  females  of  the  same  species  has  been  produced, 
which  wo  see  m  so  many  social  insects. 

But  we  have  not  as  yet  touched  on  the  climax  of  the  difE- 
culty :  namely,  the  fact  that  the  neuters  of  several  ants  differ, 
not  only  from  the  fertile  females  and  males,  but  from  each 
other,  sometimes  to  an  almost  incredible  degree,  and  are  thus 
divided  into  two  or  even  three  castes.  Tiie  castes,  moreover, 
do  not  generally  graduate  into  each  other,  but  are  perfectly 
well  defined  ;  being  as  distinct  from  each  other  as  are  any  two 
species  of  the  same  genus,  or  rather  as  any  two  genera  of  the 
same  family.  Thus  in  Eciton,  there  are  working  and  soldier 
neuters,  wnth  jaws  and  instincts  extraordinarily  difi'ercnt :  in 
Cryptocerus,  the  workers  of  one  caste  alone  carry  a  wonderful 
sort  of  shield  on  their  heads,  the  use  of  which  is  quite  imknown  : 
in  the  Mexican  JMyrmecocystus,  the  workers  of  one  caste  never 
leave  the  nest ;  they  are  fed  by  the  workers  of  another  caste, 
and  they  have  an  enormously-developed  abdomen  which  se- 
cretes a  sort  of  honey,  supplying  the  place  of  that  excreted  by 
the  aphides,  or  the  domestic  cattle,  as  they  may  be  called, 
which  our  European  ants  guard  and  imprison. 

It  will  indeed  be  thought  that  I  have  an  overweening  con- 
fidence in  the  principle  of  natural  selection,  when  I  do  not  ad- 
mit that  such  wonderful  and  Avell-established  facts  at  once  an- 
jiiliilate  the  theory.  In  the  simpler  case  of  neuter  insects  all 
of  one  caste,  which,  as  I  believe,  have  been  rendered  different 
from  the  fertile  males  and  females  through  natural  selection, 
we  may  conclude  from  the  analogy  of  ordinary  variations,  that 
the  successive,  slight,  profitable  modifications  did  not  first 
arise  in  all  the  neuters  in  the  same  nest,  but  in  some  few  alone ; 
and  that  by  the  survival  of  the  communities  with  females  which 
])r()(lure  most  neuters  having  the  advantageous  modification,  all 
the  neuters  ultimately  come  to  be  thus  characterized.  Accord- 
ing to  this  view,  Ave  ought  occasionally  to  find  in  the  same  nest 


CuAr.  YII.  OF  NATURAL  SELECTION.  229 

neuter  insects,  presenting  gradations  of  structure ;  and  this  we 
do  find,  even  frcquenth'-,  considering  liow  few  neuter  insects 
out  of  Europe  have  been  carefully  examined,  ^[r.  F.  JSinith 
lias  shown  that  the  neuters  of  several  British  ants  differ  sur- 
])risingly  from  each  other  in  size,  and  sometimes  in  color ;  and 
that  the  extreme  forms  can  be  linked  together  by  individuals 
taken  out  of  the  sanu;  nest ;  I  have  myself  compared  j^erfect 
gradations  of  this  kind.  It  sometimes  happens  that  the  larger 
or  the  smaller  sized  workers  are  the  most  numerous ;  or  that 
both  large  and  small  are  numerous,  while  those  of  an  interme- 
diate size  are  scanty  in  numbers.  Formica  flava  has  larger  and 
smaller  workers,  with  some  few  of  intermediate  size  ;  and,  in 
this  species,  as  Mr,  F.  Smith  has  observed,  the  larger  workere 
have  simj)lc  eyes  (ocelli),  which  though  small  can  be  plainly 
distinguished,  whereas  the  smaller  workers  have  their  ocelli 
rudimentary.  IlaWng  carefully  dissected  several  specimens  ot 
these  workers,  I  can  affirm  that  the  eyes  are  far  more  rudimen- 
tary in  the  smaller  workers  than  can  be  accounted  for  merely 
by  their  proportionally  lesser  size ;  and  I  fully  believe,  though 
I  dare  not  assert  so  positively,  that  the  workers  of  intermediate 
size  have  their  ocelli  in  an  exactly  intermediate  condition.  So 
that  here  we  have  two  bodies  of  sterile  workers  in  the  same 
nest,  differing  not  only  in  size,  but  in  their  organs  of  vision,  yet 
conn(^cted  by  some  few  members  in  an  intermediate  condition. 
I  may  digress  by  adding,  that  if  the  smaller  Avorkers  had  been 
the  most  useful  to  the  community,  and  those  males  and  females 
had  been  continually  selected,  which  produced  more  and  more 
of  the  smaller  workers,  until  all  the  workers  were  in  this  condi- 
tion, we  should  then  have  had  a  species  of  ant  with  neuters 
nearly  in  the  same  condition  with  those  of  Mynnica.  For  the 
workers  of  Mynnica  have  not  even  rudiments  of  ocelli,  though 
the  male  and  female  ants  of  this  genus  have  Avcll-develoi)ed 
ocelli. 

I  may  give  one  other  case  :  so  confidently  did  I  expect  to  find 
gradations  in  important  points  of  structure  between  the  differ- 
ent castes  of  neuters  in  the  same  species,  that  I  glaiUy  availed 
myself  of  Mr.  F.  Smith's  offer  of  numerous  specimens  from  the 
same?  nest  of  tlie  driver-ant  (Aiiomma)  of  West  Africa.  The 
reader  will  peihajis  best  a]i])reciate  the  amount  of  difference  in 
these  workers,  by  my  giving  not  the  actual  measurements,  but 
a  strictly  aecurate  illustration  :  the  difference  was  the  same  as 
if  we  were  to  sec  a  set  of  workmen  building  a  house,  of  whom 
many  were  five  feet  four  inches  high,  and  many  sixteen  feet 


230  OBJECTIONS  TO   THE  TIIEOPwY  Chap.  VII. 

high  ;  but  wc  must  suppose  that  the  larger  workmen  had  heads 
four  instead  of  three  times  as  l:)ig  as  those  of  the  smaller  men, 
and  jaws  nearly  five  times  as  big.  The  jaws,  moreover,  of  the 
working  ants  of  the  several  sizes  differed  wonderfully  in  shape, 
and  in  the  form  and  number  of  the  teeth.  But  the  important 
fact  f(^r  us  is,  that,  though  the  workers  can  be  grouped  into  castes 
of  different  sizes,  yet  they  graduate  insensibly  into  each  other, 
as  does  the  widely-different  structure  of  their  jaws.  I  speak 
confidently  on  this  latter  point,  as  Sir  J.  Lubbock  made  draw- 
ings for  me,  with  the  camera  lucida,  of  the  jaws  which  I  dis- 
sected from  the  workers  of  the  several  sizes.  Mr.  Bates,  in  his 
most  interesting  "Naturalist  on  the  Amazons,"  has  described 
analogous  cases. 

With  these  facts  before  me,  I  believe  that  natural  selection, 
by  acting  on  the  fertile  ants  or  parents,  could  form  a  species 
which  should  regularly  produce  neuters,  either  all  of  large  size 
with  one  form  of  jaw,  or  all  of  small  size  M-ith  jaws  having  a 
Avidely-different  structure;  or  lastl}^,  and  this  is  the  clima.x  of 
dilliculty,  one  set  of  workers  of  one  size  and  structure,  and  at 
the  same  time  another  set  of  workers  of  a  different  size  and 
structure ;  a  graduated  series  having  first  been  formed,  as  in 
the  case  of  the  driver-ant,  and  then  the  extreme  forms  having 
been  produced  in  greater  and  greater  numbers,  through  the 
survival  of  the  parents  which  generated  them,  until  none  with 
an  intermediate  structure  were  produced. 

An  analogous  explanation  has  been  given  by  Mr.  Wallace, 
of  the  equally  com[)lcx  case,  of  certain  Malayan  butterflies 
regularly  appearing  under  two  or  even  three  distinct  female 
forms  ;  and  by  Fritz  Miiller,  of  certain  Brazilian  crustaceans 
likewise  appearing  under  two  widely-distinct  male  forms.  But 
this  subject  need  not  here  be  discussed. 

I  have  now  explained  how,  as  I  believe,  the  wonderful  fact 
of  two  distinctly-defined  castes  of  sterile  workers  existing  in 
the  same  nest,  both  widely  different  from  each  other  and  from 
their  parents,  has  originated.  We  can  see  how  useful  their 
production  niay  have  been  to  a  social  comnnmity  of  ants,  on 
the  same,  principle  that  the  division  of  labor  is  useful  to  civil- 
ized man.  Ants,  however,  work  by  inherited  instincts  and  by 
inherited  organs  or  tools,  while  man  works  by  acquired  knowl- 
edge and  manufactured  instruments.  But  I  must  confess,  that, 
Avith  all  my  faith  in  natural  selection,  I  should  never  have  an- 
ticipated tiiat  this  principle  could  have  been  efficient  in  so  high 
a  degree,  had  not  the  case  of  these  neuter  insects  convinced  me 


Chap.  VII.  OF  NATURAL  SELECTION.  231 

of  the  fact.  I  have,  therefore,  discussed  this  case,  at  some  little 
but  wholly  insuniciout  length,  in  order  to  show  tlio  power  of  nat- 
ural selection,  and  likewise  because  this  is  by  far  the  most  serious 
special  dillieulty  which  my  theory  has  encountered.  The  case, 
also,  is  very  intercstinir,  as  it  proves  that  with  animals,  as  with 
plants,  any  amount  of  modification  may  be  cUc'cted  ])y  the  ac- 
cumulation o(  numerous,  slight,  spontaneous  variations,  which 
are  in  any  way  jirolitable,  without  exercise  or  hal)it  havini^ 
been  brouf^ht  into  play.  For  peculiar  hal^its  confined  to  the 
workers  or  sterile  females,  however  long  they  mif^ht  be  fol- 
lowed, could  not  possibly  affect  the  males  and  fertUe  female, 
which  alone  leave  descendants.  I  am  surprised  that  no  one 
has  hitherto  advanced  this  demonstrative  case  of  neuter  insects, 
against  the  well-known  doctrine  of  inherited  habit,  as  advanced 
by  Lamarck. 

iSummari/. 

I  have  endeavored  in  this  chapter  briefly  to  show  that  the 
mental  qualities  of  our  domestic  animals  vary,  and  that  the  vari- 
ations are  inlierited.  Still  more  briefly  I  have  attempted  to  show 
that  instincts  A'ary  slightly  in  a  state  of  nature.  No  one  will 
dispute  that  instincts  are  of  the  highest  importance  to  each 
animal.  Therefore  there  is  no  real  diiliculty,  under  changing 
conditions  of  life,  in  natural  selection  accumulating  to  any  ex- 
tent slight  modifications  of  instinct  which  are  in  any  way  use- 
ful. In  some  cases  habit  or  use,  and  disuse,  have  proliably  come 
into  play.  I  do  not  pretend  that  the  facts  given  in  this  chapter 
strengthen  in  any  great  degree  my  theory ;  but  none  of  the 
cases  of  diiliculty,  to  the  best  of  my  judgment,  annihilate  it. 
On  the  other  hand,  the  fact  that  instincts  are  not  always  ab- 
solutely perfect,  and  are  liable  to'mistakes ;  that  no  instinct 
can  be  shown  to  have  been  produced  for  the  good  of  other 
animals,  tliough  animals  take  advantage  of  the  instincts  of 
others;  that  tlie  canon  in  natural  history  of  "  Natura  non  facit 
saltuin,"isap]ili(able  to  instincts  as  well  as  to  corporeal  struct- 
ure, and  is  plainly  explicable  on  the  foregoing  views,  but  is 
otherwise  inexplicable — all  tend  to  corroborate  the  theory  of 
natural  selection. 

This  theory  is,  also,  strengthened  by  some  few  other  facts  in 
regard  to  instincts ;  as  by  that  common  case  of  closely-allied, 
but  distinct,  species,  when  inhabiting  distant  parts  of  the 
world  and  living  under  considerably  diffcM-ent  conditions  of 
lifCj  yet  often  retaining  nearly  the  same  instincts.    For  instance, 


232  SUMMARy.  Chap.  VII. 

we  can  understand,  on  the  principle  of  inheritance,  how  it  is 
that  the  thrush  of  tropical  South  America  hues  its  nest  -with 
mud,  in  the  same  peculiar  manner  as  docs  our  British  thrush : 
how  it  is  that  the  liornbills  of  Africa  and  India  have  the  same 
extraordinary  instinct  of  plastering'  up  and  imprisoning  the 
females  in  a  hole  in  a  tree,  with  only  a  small  hole  left  in  the 
plaster  throug-h  Avhich  the  males  feed  them  and  the  young 
Avhen  hatched :  how  it  is  that  the  male  wrens  (Troglodytes)  of 
North  America  build  "cock-nests,"  to  roost  in,  like  the  males 
of  our  kitty-wrens — a  habit  wholly  unlike  that  of  any  other 
known  bird.  Finally,  it  may  not  be  a  logical  deduction,  but 
to  my  imagination  it  is  far  more  satisfactory  to  look  at  such 
instincts  as  the  young  cuckoo  ejecting  its  foster-brothers — ants 
making  slaves — the  lnrva3  of  ichneumonidas  feeding  within  the 
live  bodies  of  caterj:)illars — not  as  specially  endowed  or  created 
instincts,  but  as  small  consequences  of  one  general  laAV,  lead- 
ing to  the  advancement  of  all  organic  beings — namely,  multi- 
ply, vary,  let  the  strongest  live  and  the  weakest  die. 


Ci:\v.  Vlil.  lIYBiaDISM.  23J 


CHAPTER  VIII. 

IIYBKIDISM. 

Distinction  Ijctwpon  the  Stcrilifir  of  First  CropfCF  and  of  Hybrids— Slorilil.v  various 
in  JX'iXTCf,  nut  uiiivtM>jil.  all'i'ctcd  l)y  cIojji!  Interbrccdincr,  removed  by  Domesti- 
cation—Lawf  LTovi'miiiL,'  llie  Sterility  of  Hybrids— Sterility  not  a  special  Endow- 
ment, bat  incidental  on  oilier  DilTerences,  not  accnmiilated  by  Natural  Selection 
— Causes  of  the  Sterility  f)f  First  Crosses  and  of  Hybrids— i'urallilisrn  between 
llie   Ell'ectrt  of  Clianjred  Conditions  of  Life  and  of  Crossin;,'— Diinnrnldsm  and 

,  Triuiorpliism — Fertility  of  Varieties  when  crossed  and  of  their  Monjirel  Ollsprinij 
not  universal— Hybrids  and  Mongrels  compared  independently  of  tlicir  Fertility 
—Summary. 

The  view  generally  entertained  by  naturalists  is  that 
species,  when  intercrossed,  have  been  specially  endowed  witli 
sterility,  in  order  to  prevent  their  confusion.  This  view  cer- 
tainly seems  at  first  hifi;hly  pro])able,  for  s])ecies  within  the 
same  country  could  hardly  have  been  kept  distinct  had  they 
been  capable  of  freely  crossing-.  The  subject  is  in  many  ways 
important  for  us,  more  especially  as  the  sterility  of  species 
when  first  crossed,  and  that  of  tlieir  hybrid  offspring,  cannot 
have  been  acquired  by  the  continued  preservation  of  successive, 
]irolit:d)lc  degrees  of  sterility.  It  is,  as  I  hope  to  show,  inci- 
dental on  differences  in  tlie  reproductive  system  of  the  jiarciit- 
spceics,  and  is  not  cither  a  specially  acquired  or  endoAVcd 
quality. 

In  treating  this  subject,  two  classes  of  facts,  to  a  large  ex- 
tent fundamentally  different,  have  generally  been  confounded 
together ;  namely,  the  sterility  of  two  species  when  first  crossed, 
antl  the  sterility  of  the  hybrids  produced  from  them. 

Pure  species  have  of  course  their  organs  of  reproduction  in 
a  perfect  condition,  yet  when  intercrossed  they  produce  either 
few  or  no  offs])ring.  Hybrids,  on  the  other  hand,  have  their 
reproductive  organs  functionally  impotent,  as  may  ])e  dearly 
seen  in  the;  statt;  of  the  malt;  element  in  both  ])hints  and  ani- 
mals ;  though  the  formative;  organs  themselves  are  perfect  in 
structure,  as  far  as  the  microscope  reveals.  In  the  first  case 
the  two  sexual  elements  which  go  to  form  the  embryo  are  per- 


234  DEGKEES   OF  STERILITY.  Chap.  YIII. 

feet ;  in  the  second  case  they  are  either  not  at  all  developed, 
or  are  imperfectly  developed.  This  distinction  is  important, 
■when  the  cause  of  the  sterility,  -which  is  common  to  the  two 
cases,  has  to  be  considered.  The  distinction  probably  has  been 
slurred  over,  owiniii;  to  the  sterility  in  botli  cases  being'  looked 
on  as.  a  special  endowment,  Ijoyond  the  province  of  our  reason- 
ing powers. 

The  fertility  of  vaiietics,  that  is  of  the  forms  known  or  be- 
lieved to  have  descended  from  common  parents,  when  inter- 
crossed, and  likewise  the  fertility  of  their  mongrel  offspring,  is, 
with  reference  to  my  theory,  of  equal  importance  with  the 
sterility  of  species  ;  for  it  seems  to  make  a  broad  and  clear  dis- 
tinction between  varieties  and  species. 

Defjrees  of  Sterility. — First,  for  the  sterility  of  species  when 
crossed  and  of  their  hybrid  offspring.  It  is  impossible  to  study 
the  several  memoirs  and  works  of  those  two  conscientious  and 
admirable  observers,  Kolrcuter  and  Gartner,  who  almost  de- 
voted their  lives  to  this  subject,  without  being  deeply  im- 
pressed with  the  high  generality  of  some  degree  of  steriUty. 
Kolreuter  makes  the  rule  universal ;  but  then  he  cuts  the  knot, 
for  in  ten  cases  in  which  he  found  two  forms,  considered  by 
most  authors  as  distinct  species,  quite  fertile  together,  he  un- 
hesitatingly ranks  them  as  varieties.  Gartner,  also,  makes  the 
rule  equally  universal ;  and  he  disputes  the  entire  fertility  of 
Kolrcuter's  ten  cases.  But  in  these  and  in  many  other  cases, 
Gartner  is  obliged  carefully  to  count  the  seeds,  in  order  to 
show  that  there  is  any  degree  of  sterility.  He  always  compares 
the  maximum  number  of  seeds  produced  by  two  species  when 
first  crossed,  and  the  maximum  produced  by  their  hybrid  off- 
spring, with  the  average  number  produced  by  both  pure  par- 
ent-species in  a  state  of  nature,  lint  a  serious  cause  of  error 
seems  to  me  to  be  here  introduced  :  a  plant,  to  be  hybridized, 
nuist  be  castrated,  and  Avhat  is  often  more  imjiortant,  must  be 
secluded  in  order  to  prevent  pollen  being  brought  to  it  by  in- 
sects from  other  plants.  Nearly  all  the  plants  experimented 
on  by  Gartner  were  potted,  and  were  kept  in  a  chamber  in  his 
house.  That  these  processes  are  often  injurious  to  the  fertility 
of  a  plant  cannot  be  doubted ;  for  Giirtner  gives  in  his  table 
about  a  score  of  cases  of  plants  Avhich  he  castrated,  and  arti- 
ficially fertilized  with  their  own  pollen,  and  (excluding  all  cases 
such  as  the  Leguminosa',  in  which  there  is  an  acknowledged 
difliculty  in  the  manipidation)  half  of  these  twenty  plants  had 
their  fertility  in  some  degree  impaired.     Moreover,  as  Giirlncr 


Chap.  VIII.  DEGREES  OF  STERILITY.  235 

ropcalcdly  cnissed  some  forms,  such  as  the  common  red  and 
blue  pimpernels  (Anagallis  arvensis  and  ccerulea),  wliicli  the 
best  botanists  rank  as  varieties,  and  found  them  absolutely 
sterile,  -sve  may  doubt  whether  many  species  are  really  so  ster- 
ile, when  intercrossed,  as  he  believed. 

It  is  certain,  on  the  one  hand,  that  the  sterility  of  various 
species  "when  crossed  is  so  dilferent  in  deg'ree  and  graduates 
away  so  insensibly,  and,  on  the  other  hand,  that  the  fertility 
of  pure  sjiecies  is  so  easily  aflected  by  various  circumstances, 
that  for  all  practical  purposes  it  is  most  difficult  to  say  where 
perfect  fertility  ends  and  sterility  begins.  I  think  no  better 
evidence  of  this  can  be  required  than  that  the  two  most  ex- 
perienced observers  who  have  ever  lived,  namely,  Kolrcuter 
and  Gartner,  should  luivc  arrived  at  diametrically  opposite  con- 
clusions in  regard  to  the  very  same  species.  It  is  also  most 
instructive  to  compare — but  I  have  not  space  here  to  enter  on 
details — the  evidence  advanced  by  our  best  botanists  on  the 
question  whether  certain  doubtful  forms  should  be  ranked  as 
species  or  varieties,  with  the  evidence  from  fertility  adduced 
by  different  hybridizers,  or  by  the  same  author,  from  ex])eri- 
ments  made  during  different  years.  It  can  thus  be  shown  that 
neither  sterility  nor  fertility  alfords  any  clear  distinction  ];c- 
tween  species  and  varieties;  but  tliat  the  evidence  from  this 
source  graduates  away,  and  is  doubtful  in  the  same  degree  as 
is  the  evidence  derived  from  other  constitutional  and  structural 
differences. 

In  regard  to  the  sterility  of  hybrids  in  successive  generations; 
though  Giirtner  was  enabled  to  rear  some  hybrids,  carefully 
guarding  them  from  a  cross  with  either  pure  parent,  for  six  or 
seven,  and  in  one  case  for  ten  generations,  yet  he  asserts  posi- 
tively that  their  fertility  never  increased,  but  generally  de- 
creased greatly  and  suddenly.  With  respect  to  this  decrease, 
it  may  first  be  noticed  that,  when  any  deviation  in  structure  or 
constitution  is  common  to  both  parents,  this  is  often  transmitted 
in  an  augmented  degree  to  the  oiTspring;  and  both  sexual  ele- 
ments in  hyljritl  ])lants  are  already  allected  in  some  degree. 
15ut  I  believe  in  nearly  all  these  cases,  that  the  fertility  has 
been  diminished  by  an  independent  cause,  namely,  by  too  close 
interbreeding.  I  have  collected  so  large  a  body  of  facts,  show- 
ing on  the  one  liand  that  an  occasional  cross  with  a  distinct 
individual  or  variety  increases  the  vigor  and  fertility  of  the 
offspring,  and  on  the  other  hand  that  very  clc>8e  interbreeding 
lessons  their  vigor  and  fcrtihty,  that  I  must  admit  the  correct- 


23G  DEGREES  OF  STERILITY.  Cu.vp.  VIII. 

ness  of  this  almost  universal  belief  among  breeders.  Hybrids 
are  seldom  raised  b}--  experimentalists  in  great  numl)ers ;  and 
as  the  parent-species,  or  other  allied  hybrids,  generally  grow 
in  the  same  garden,  the  visits  of  insects  must  be  carefully  pre- 
vented during  the  ilowering  season:  hence  hyljrids  will  gener- 
ally have  to  be  fertilized  during  each  generation  by  their  own 
individual  pollen  ;  and  this  would  probably  be  injurious  to  their 
fertility,  already  lessened  by  their  hybrid  origin.  I  am  strength- 
ened in  this  conviction  by  a  remarkable  statement  repeatedly 
made  by  Giirtner,  namely,  that  if  even  the  less  fertile  hybrids 
be  artilicially  fertilized  with  hybrid  pollen  of  the  same  kind, 
tlieir  fertility,  notwithstanding  the  frequent  ill  elFects  from 
manipulation,  sometimes  decidedly  increases,  and  goes  on  in- 
creasing. Now,  in  the  process  of  ai'tilicial  fertilization,  pollen 
is  as  often  taken  by  chance  (as  I  know  from  my  own  experi- 
vncc)  from  the  anthers  of  another  tlower,  as  from  the  anthers 
of  the  tlower  itself  which  is  to  be  fertilized ;  so  that  a  cross  be- 
tween two  flowers,  though  probably  often  on  the  same  plant, 
would  be  thus  etfected.  Moreover,  whenever  complicated  ex- 
jieriments  are  in  jirogress,  so  careful  an  observer  as  Gartner 
would  have  castrated  his  hybrids,  and  this  wovdd  have  insured 
in  each  generation  a  cross  with  pollen  from  a  distinct  tlower, 
either  from  the  same  plant  or  from  another  plant  of  the  same 
hj'brid  nature.  And  thus  the  strange  fact  of  an  increase  of 
fertility  in  the  successive  generations  of  art tficicdhf -fertilized 
hylirids,  in  contrast  Avith  those  spontaneously  self-fertilized, 
may,  as  I  believe,  be  accounted  for  by  too  close  interbreeding 
having  been  avoided. 

Now  let  us  turn  to  the  results  arrived  at  l)y  a  third  most 
experienced  hybridizer,  namely,  the  Hon.  and  Rev.  W.  Herbert. 
He  is  as  emphatic  in  his  conclusion  that  some  hybrids  are  per- 
fectly fertile — as  fertile  as  the  pure  parent-species — as  are  Kiil- 
rcuter  and  Gartner  that  some  degree  of  sterility  between  dis- 
tinct species  is  a  imiversal  law  of  Nature.  He  experimented 
on  some  of  the  very  same  species  as  did  Gartner,  The  diflVr- 
ence  in  their  results  may,  I  think,  be  in  part  accounted  for  by 
Herliert's  great  horticultural  skill,  and  by  his  having  hot-houses 
at  his  command.  Of  his  many  important  statements  I  will  here 
give  only  a  single  one  as  an  examjile,  namcdy,  that  "  every 
ovule  in  a  pod  of  Crinum  capense  fertilized  by  C.  revolutuni 
])roduced  a  plant,  which  I  never  saw  to  occur  in  a  case  of  its 
natural  fecundation."  So  that  here  wc  have  perfect,  or  even 
more  than  commonly  perfect,  fertility  in  a  first  cross  between 
two  distinct  species. 


Chap.  VIII.  DEGREES  OF  STEKILITY.  237 

This  case  of  tlie  Crinum  leads  me  to  refer  to  a  singular  fact, 
namely,  that  individual  plants  of  certain  species  of  Lobelia, 
Vcrbascuni,  and  Passillora,  can  easily  be  fertilized  by  pollen 
from  a  distinct  species,  but  not  by  pollen  from  the  same;  plant, 
though  this  pollen  can  be  proved  to  l)e  perfectly  sound  by  fer- 
tilizing other  plants  or  species.  In  the  genus  llippeastrum,  in 
Corydalis  as  shown  by  Prof.  Hildebrand,  in  various  orchids  as 
shown  by  Mr.  Scott  and  Fritz  Mliller,  all  the  individuals  are  in 
this  })eculiar  condition.  So  that  with  some  species,  certain 
abnormal  individuals,  and  in  other  species  all  the  individuals, 
can  actually  be  hybridized  much  more  readily  than  they  can 
be  fertilized  by  jiollen  from  the  same  individual  plant !  To 
give  one  instance,  a  bulb  of  llippeastrum  aulicum  produced  four 
flowers  ;  three  were  ferlilizod  by  Herbert  with  their  own  pollen, 
and  the  fourth  was  subsequently  fertilized  by  the  pollen  of  a 
compound  hybrid  descended  from  three  distinct  species:  the 
result  was,  that  "  the  ovaries  of  the  first  three  flowers  soon 
ceased  to  grow,  and  after  a  few  days  perished  entirely,  whereas 
the  pod  impregnated  by  the  pollen  of  the  hybrid  made  vigorous 
growth  and  rapid  progress  to  maturity,  and  bore  good  seed, 
which  vegetated  freely."  Mr.  Herbert  tried  similar  experi- 
ments during  many  y(iars,  and  always  with  the  same  result. 
With  those  plants  in  which  certain  individuals  alone  fail  to  be 
fertilized  by  their  own  pollen,  though  thej^  appear  cjuite  healthy 
and  although  both  ovules  and  pollen  are  perfectly  good  with 
reference  to  other  species,  yet  they  must  be  in  some  way  in  an 
unnatural  condition.  Tliese  cases  serve  to  show  on  what  slight 
and  mysterious  causes  the  lesser  or  greater  fertility  of  a  species 
sometimes  depends. 

The  practical  experiments  of  horticulturists,  though  not 
made  with  scientific  ])recision,  deserve  some  notice.  It  is  no- 
torious in  how  complicated  a  manner  the  species  of  Pelargo- 
nium, Fuchsia,  Calceolaria,  Petunia,  Rhododendron,  etc.,  have 
been  crossed,  yet  many  of  these  hybrids  seed  freely.  For  in- 
stance, Herbert  asserts  that  a  hybrid  from  Calceolaria  integri- 
folia  and  jilanlaginea,  species  most  widely  dissimilar  in  general 
habit,  "reproduced  itself  as  perfectly  as  if  it  had  been  a  natu- 
ral species  from  the  mountains  of  Chili."  I  have  taken  some 
pains  to  ascertain  the  degree  of  fertility  of  some  of  the  complex 
crosses  of  Khod(jdendrons,  and  I  am  assured  that  many  of  thcrn 
are  perfectly  fertile.  Mr.  C.  Noble,  for  instance,  informs  mc 
that  he  raises  stocks  for  grafting  from  a  hvbrid  between  Rhod. 
Poiifieiiin  and  Catawbiense,  and  that  this  hybrid  "seeds  as 


238  DEGREES  OF  STEKILITY.  Chat.  VIII. 

freely  as  it  is  possible  to  imac^ine."  Had  liybrids,  when  fairly 
treated,  always  p^ono  on  decreasing  in  fertility  in  each  succes- 
sive generation,  as  Gartner  believed  to  be  the  case,  the  fact 
would  have  been  notorious  to  nursery-men.  Horticulturists 
raise  large  beds  of  the  same  hybrids,  and  such  alone  are  fairly 
treated,  for  by  insect-agency  the  several  individuals  of  the 
same  hybrid  variety  are  allowed  to  freely  cross  with  each  other, 
and  the  injurious  influence  of  close  interbreeding  is  thus  ]irc- 
vented.  Any  one  may  readily  convince  himself  of  the  eih- 
ciency  of  insect-agency  by  examining  the  lloAvers  of  the  more 
sterile  kinds  of  hybrid  Rhododendrons,  which  produce  no  pol- 
len, for  he  will  find  on  their  stigmas  plenty  of  pollen  brought 
from  other  flowers. 

In  regard  to  animals,  much  fewer  experiments  have  been 
carefully  tried  than  with  jilants.  If  our  systematic  arrange- 
ments can  be  trusted,  that  is,  if  the  genera  of  animals  are  as 
distinct  from  each  other  as  are  the  genera  of  plants,  then  we 
may  infer  that  animals  more  widely  separated  in  the  scale  of 
Nature  can  be  more  easily  crossed  than  in  the  case  of  plants ; 
l)ut  the  hybrids  themselves  are,  I  think,  more  sterile.  1  doubt 
whether  any  case  of  a  perfectly-fertile  hybrid  animal  can  be 
considered  as  thoroughly  well  authenticated.  It  should,  how- 
ever, be  borne  in  mind  that,  owing  to  few  animals  breeding 
freely  under  confinement,  few  experiments  have  been  fairly 
tried :  for  instance,  the  canary-bird  has  been  crossed  Avith  nine 
other  finches,  but,  as  not  one  of  these  nine  species  breeds 
freely  in  confinement,  we  have  no  right  to  expect  that  the  first 
crosses  between  them  and  the  canary,  or  that  their  Inbrids, 
should  be  perfectly  fertile.  Again,  with  resjiect  to  the  fertility 
in  successive  generations  of  the  more  fertile  hybrid  animals, 
1  hardly  know  of  an  instance  in  which  two  fiimilies  of  the  same 
hyl>rid  have  been  raised  at  the  same  time  from  difierent  par- 
ents, so  as  to  avoid  the  ill-effects  of  close  interbreeding.  On 
the  contrary,  brothers  and  sisters  have  usually  been  crossed 
in  each  STiccessive  generation,  in  opposition  to  the  constantly- 
repeated  admonition  of  every  breeder.  And  in  this  case,  it  is 
not  at  all  surprising  that  the  inherent  sterility  in  the  hybrids 
should  have  gone  on  increasing.  If  we  were  to  act  thus,  and 
pair  brothers  and  sisters  in  the  case  of  any  pure  animal,  which 
from  any  cause  had  the  least  tendency  to  sterility,  the  breed 
would  assuredly  be  lost  in  a  few  generations. 

Although  I  do  not  know  of  any  thoroughly  well-autlienli- 
catcd  cases  of  perfectly-fertile  liybrid  animals,  I  have  reason  to 


Chap.  Vlll.  DEGREES  OF  STERILITY.  239 

believe  that  tlio  liyl)ri(ls  from  Cervulus  vaginalis  and  Rccvesii, 
and  from  Pliasianus  colchicus  with  P.  toniuatus,  arc  perfectly 
fertile.  It  has  lately  been  asserted  in  France,  that  two  such 
distinct  species  as  the  hare  and  the  raljbit,  Avhen  they  can  be 
|Tot  to  breed  together,  produce  offspring,  which  are  highly  fer- 
tile when  crossed  with  one  of  the  parent-species.  The  hybrids 
from  the  common  and  Chinese  geese  (A.  cygnoides),  species 
which  are  so  dillerent  that  they  are  generally  ranked  in  dis- 
tinct genera,  have  often  bred  in  this  country  with  either  pure 
parent,  and,  in  one  single  instance,  they  have  bred  inter  se.  This 
was  eifected  by  Mr.  Eyton,  who  raised  two  hybrids  from  the 
same  parents,  but  from  difVerent  hatches ;  and  from  these  two 
birds  he  raised  no  less  than  eight  hybrids  (grandchildren  of  the 
pure  geese)  from  one  nest.  In  India,  however,  these  cross-bred 
geese  must  be  far  more  fertile ;  for  I  am  assured  by  two  emi- 
nently-capable judges,  namely,  Mr.  Blyth  and  Captain  Hutton, 
that  whole  flocks  of  these  crossed  geese  are  kept  in  various 
parts  of  the  country ;  and  as  they  are  kept  for  profit,  where 
neither  pure  parent-species  exists,  they  must  certainly  be  high- 
ly or  perfectly  fertile. 

Tlie  various  races  of  each  kind  of  domesticated  animals  are 
quite  fertile  when  crossed  together ;  yet  in  many  cases  they 
are  descended  from  two  or  more  wild  species.  From  this  fact 
wc  must  conclude  either  that  the  aboriginal  parent-species 
produced  at  first  perfectly  fertile  hybrids,  or  that  the  hybrids 
subsequently  reared  under  domestication  became  quite  fertile. 
This  latter  alternative,  which  was  first  propounded  by  Pallas, 
seems  tlie  most  probable,  and  can,  indeed,  hardly  be  doubted. 
It  is,  for  instance,  almost  certain  that  our  dogs  are  descended 
from  several  wild  stocks ;  yet,  witli  perhaps  the  exception  of 
certain  indigenous  domestic  dogs  of  South  America,  all  are 
quite  fertile  together;  and  anahigy  makes  me  greatly  doubt 
whether  the  several  aljoriginal  species  would  at  first  have 
freely  bred  together,  and  have  produced  quite  fertile  hybrids. 
So,  again,  I  have  lately  acquired  decisive  evidence  tliat  the 
crossed  offspring  from  the  Indian  humped  and  common  cattle 
are  inter  se  perfectly  fcrtih^;  and  from  the  observations  by 
Ililtimeyer  on  their  important  osteijlogical  differences,  as  well 
as  from  tliose  by  Mr.  IJlytli  on  their  differences  in  habits,  voice, 
constitution,  etc.,  these  two  forms  must  be  regarded  as  good 
and  distinct  species  as  any  in  the  world.  According  to  this 
view  of  the  origin  of  many  domestic  animals,  we  must  either 
give  up  tlie  belief  of  the  almost  universal  sterility  of  distinct 


240  LAWS  GOVERNING  THE  STERILITY  Chap.  VIII. 

species  of  animals  when  crossed ;  or  we  must  look  at  sterility, 
not  as  an  indelible  characteristic,  but  as  one  capable  of  being 
removed  by  domestication. 

Finally,  considering^  all  the  ascertained  facts  on  the  inter- 
crossing of  plants  and  animals,  it  may  be  concluded  that  some 
degree  of  sterility,  both  in  first  crosses  and  in  hybrids,  is  an 
extremely  general  result ;  but  that  it  cannot,  under  our  present 
state  of  knowledge,  be  considered  as  absolutely  univ'crsal. 

Laics  f/overnlng  the  Sterility  of  First  Grosses  and  of  Hybrids. 

We  will  now  consider  a  little  more  in  detail  the  circum- 
stances and  rules  governing  the  sterility  of  first  crosses  and  of 
hybrids.  Our  chief  object  will  be  to  see  whether  or  not  the 
rules  indicate  that  species  have  specially  been  endowed  with 
this  quality,  in  order  to  prevent  their  crossing  and  blending  to- 
gether in  utter  confusion.  The  following  rules  and  conclusions 
are  chiefly  drawn  \\\)  from  Gartner's  admirable  work  on  the 
hybridization  of  plants.  I  have  taken  much  pains  to  ascertain 
how  far  the  rules  apply  to  animals,  and,  considering  how  scanty 
our  knowledge  is  in  regard  to  hybrid  animals,  I  have  been  sur- 
prised to  find  how  generally  the  same  rules  apply  to  both  king- 
doms. 

It  has  been  already  remarked,  that  the  degree  of  fertilitj'', 
both  of  first  crosses  and  of  hybrids,  graduates  from  zero  to  per- 
fect fertility.  It  is  surprising  in  how  many  curious  ways  this 
gradation  can  be  shown ;  but  only  the  barest  outline  of  the 
facts  can  here  be  given.  When  pollen  from  a  ])lant  of  one 
family  is  placed  on  the  stigma  of  a  plant  of  a  distinct  family,  it 
exerts  no  more  influence  than  so  much  inorganic  dust.  From 
this  absolute  zero  of  fertility,  the  pollen  of  dilferent  species  of 
the  same  genus  applied  to  the  stigma  of  some  one  of  the 
species,  3-ields  a  jierfect  gradation  in  the  number  of  seeds  pro- 
duced, up  to  nearly  comj)lete  or  even  quite  comi)lete  fertility ; 
and,  as  we  have  seen,  in  certain  abnormal  cases,  even  to  an 
excess  of  fertility,  beyond  tiiat  which  the  plant's  own  pollen 
j^roduces.  So  in  hybrids  themselves,  there  are  some  which 
never  have  produced,  and  probably  never  would  produce,  even 
with  the  pollen  of  the  pure  parents,  a  single  fertile  seed  :  but 
in  some  of  these  cases  a  first  trace  of  fertility  mvcy  be  detected, 
by  the  jiollen  of  one  of  the  pure  parent-sjiecies  causing  the 
flower  of  the  hybrid  to  wither  earlier  than  it  otherwise  would 
have  done  ;  and  the  early  withering  of  the  flower  is  well  known 


Chap.  VIII.       OF  FIRST  CROSSES  AND   OF  HYBRIDS.  241 

to  be  a  sign  of  incipient  fertilization.  From  this  extreme  degree 
of  sterility  wc  have  self-fertilized  hybrids  jiroduting  a  greater 
and  greater  number  of  seeds  up  to  perfect  fertility, 

Hyljrids  from  two  species  which  are  very  difiicult  to  cross, 
and  which  rarely  produce  any  offspring,  are  generally  very 
sterile ;  but  the  parallelism  between  the  dilliculty  of  making  a 
first  cross,  and  the  sterility  of  the  hybrids  thus  jiroduced — two 
classes  of  facts  which  are  generall}-  confounded  together — is  by 
no  means  strict.  There  are  many  cases,  in  Avhich  two  pure 
species,  :is  in  the  genus  Yerbascum,  can  be  united  with  un- 
usual facility,  and  produce  numerous  hybrid-offspring,  yet  these 
hybrids  are  remarkabh'  sterile.  On  the  other  hand,  there  are 
sp(M-ies  which  can  be  crossed  very  rarelv,  or  with  extreme  diflli- 
culty,  but  the  hybrids,  ■when  at  last  produced,  are  very  fertile. 
Even  within  the  limits  of  the  same  genus,  for  instance  in  Dian- 
thus,  these  two  opj^osite  cases  occur. 

•  The  fertility,  both  of  first  crosses  and  of  hybrids,  is  more 
easily  affected  by  unfavorable  conditions,  than  is  the  fertility 
of  pure  species.  But  the  degree  of  fertility  is  likewise  innately 
variable  ;  for  it  is  not  always  the  same  when  the  same  two 
species  arc  crossed  under  the  same  circumstances,  but  depends 
in  part  upon  the  constitution  of  the  individuals  which  happen 
to  have  been  chosen  for  the  experiment.  So  it  is  with  hybrids, 
for  their  degree  of  fertility  is  often  found  to  differ  greatly  in 
the  several  individuals  raised  from  seed  out  of  the  same  ca})sule 
and  exposed  to  the  same  conditions. 

By  the  term  systematic  affinity  is  meant,  the  resemblance 
between  species  in  structure  and  in  constitution,  more  espe- 
cially in  the  structure  of  parts  which  are  of  high  physiological 
importance  and  which  differ  little  in  the  allied  sjiecies.  Now 
the  fertility  of  fust  crosses  between  species,  and  of  the  hybrids 
protluced  from  them,  is  largely  governed  by  their  systematic 
affmity.  This  is  clearly  shown  by  hybrids  never  having  lieen 
raised  l)etween  species  ranked  by  systematists  in  distinct  fami- 
lies ;  and,  on  the  other  hand,  by  very  closely-allied  species  gener- 
ally uniting  Mith  facility.  But  the  correspondence  between 
systematic  affmit}-  and  the  facility  of  crossing  is  by  no  means 
strict,  A  nudtitude  of  cases  could  be  given  of  very  closely- 
allied  species  which  Avill  not  imite,  or  only  with  extreme  diffi- 
culty ;  and,  on  the  other  hand,  of  very  distinct  species  which 
unite  with  the  utmost  facility.  In  the  same  family  there  may 
be  a  genus,  as  Dianthus,  in  which  very  many  species  can  most 
readilv  be  crossed  ;  and  another  genus,  as  ISilcne,  in  which  the 
II 


242  LAWS  GOVERNING  THE  STERILITY         Chap.  VIIL 

most  persevering  efforts  have  failed  to  produce  between  ex- 
tremely-close species  a  single  hybrid.  Even  within  the  limits 
of  the  same  genus,  wc  meet  with  this  same  difference  ;  for  in- 
stance, the  many  species  of  Nicotiana  have  been  more  largely 
crossed  than  the  species  of  almost  any  other  genus  ;  but  Giirt- 
ner  found  that  N.  acuminata,  which  is  not  a  particularly  dis- 
tinct species,  obstinately  failed  to  fertilize,  or  to  be  fertilized 
by,  no  less  than  eight  other  species  of  Nicotiana.  Many  analo- 
gous facts  could  be  given. 

No  one  has  been  able  to  point  out  what  kind,  or  what 
amount,  of  difference  in  any  recognizalile  character  is  suflicient 
to  prevent  two  species  crossing.  It  can  be  shown  that  plants 
most  Avidely  different  in  habit  and  general  appearance,  and 
having  strongly-marked  differences  in  every  part  of  the  flower, 
even  in  the  pollen,  in  the  fruit,  and  in  the  cotyledons,  can  be 
crossed.  Annual  and  perennial  plants,  deciduous  and  ever- 
green trees,  plants  inhabiting  difl'erent  stations  and  fitted  for 
extremely  different  climates,  can  often  be  crossed  with  ease. 

By  a  reciprocal  cross  between  two  species,  I  mean  the  case, 
for  instance,  of  a  stallion-horse  being  first  crossed  with  a  fe- 
male-ass, and  then  a  male-ass  with  a  mare :  these  two  species 
may  then  be  said  to  have  been  reciprocally  crossed.  There  is 
often  the  widest  possible  difference  in  the  facility  of  making 
reciprocal  crosses.  Such  cases  are  highly  important,  for  they 
prove  tliat  the  capacity  in  any  two  species  to  cross  is  often 
completely  independent  of  their  systematic  affinity,  or  of  any 
difference  in  their  whole  organization,  except  in  their  rej^ro- 
ductive  systems.  The  diversity  of  result  in  reciprocal  crosses 
between  the  same  two  species  was  long  ago  observed  by  Kiil- 
reuter.  To  give  an  instance  :  Mirabilis  jalapa  can  easily  be 
fertilized  by  the  pollen  of  M.  longiflora,  and  the  hybrids  thus 
25roduced  are  suiliciontly  fertile  ;  but  Kolreuter  tried  more  than 
two  hundred  times,  during  eight  following  j-ears,  to  fertilize 
reciprocally  M,  longiflora  v»itli  the  pollen  of  ^I.  jalapa,  and 
utterly  failed.  Several  other  equally  striking  cases  could  be 
given.  Thuret  has  observed  the  same  fact  with  certain  sea- 
weeds or  Fuci.  Gartner,  moreover,  found  that  this  difference 
of  facility  in  making  reciprocal  crosses  is  extremely  common  in 
a  lesser  degree.  He  has  observed  it  even  l)etween  closely-re- 
lated forms  (as  Matthiola  annua  and  glabra)  which  many  bota- 
nists rank  only  as  varieties.  It  is  also  a  remarkable  fact,  that 
hybrids  raised  from  reciprocal  crosses,  though  of  course  com- 
pounded of  the  very  same  two  species,  fhe  one  species  having 


Chap.  VIII.        OF  FIRST   CIJOSSES  AND   OF  HYBRIDS.  243 

first  been  used  as  the  ftithcr  and  tlien  as  the  mot  her,  though 
thev  rarely  ditFer  in  external  characters,  yet  generally  difier  in 
fertility  in  a  small,  and  oeeasionally  in  a  high  degree. 

Several  other  singular  rules  could  be  given  iVom  Gartner  ; 
for  instance,  some  species  have  a  remarkable  power  of  crossing 
with  other  species  ;  other  species  of  tlie  same  genus  have  a  re- 
markablt;  power  of  impressing  their  likeness  on  their  hybrid 
ollspring ;  but  these  two  powers  do  not  at  all  necessarily  go 
together.  There  are  certain  hybrids  which,  instead  of  having, 
as  is  usual,  an  intermediate  character  between  their  two  par- 
(mts,  always  closely  resemble  one  of  them  ;  and  such  hybrids, 
tliougli  externally  so  like  one  of  their  pure  parent-species,  are 
witli  rare  exceptions  extremely  sterile.  So  again  among  hy- 
brids which  arc  usuall}' intermediate  in  structure  between  their 
jiarents,  exceptional  and  abnormal  individuals  sometimes  are 
l)orn,  Avhich  closely  resemble  one  of  their  pure  parents;  and 
these  hybrids  are  almost  always  utterly  sterile,  even  Avhen  the 
other  hybrids  raised  from  seed  from  tlie  same  capsule  have  a 
considerable  degree  of  fertility.  These  facts  .show  how  com- 
pletely fertility  in  the  hybrid  is  independent  of  its  external 
lesemblance  to  either  pure  parent. 

Considering  the  several  rules  now  given,  Avhich  govern  the 
fertility  of  first  crosses  and  of  hybrids,  we  see  that  when  forms, 
wliich  must  be  considered  as  good  and  distinct  species,  are 
united,  tlieir  fertility  graduates  from  zero  to  perfect  fertility. 
<ir  even  to  fertility  iinder  certain  conditions  in  excess ;  that 
their  fertility,  besides  being  eminently  susceptible  to  favorable 
and  imfavorable  conditions  is  innately  variable  ;  that  it  is  by 
no  means  always  the  same  in  degree  in  the  first  cross  and  in 
th(>  hybrids  produced  from  this  cross  ;  that  the  fertility  of  hy- 
brids is  not  related  to  the  degree  in  which  the}'  resemljle  in 
external  appearance  either  parent ;  and,  lastly,  that  the  facili- 
ty of  making  a  first  cross  between  any  two  species  is  not  al- 
ways governed  by  their  systematic  aiHnity  or  degree  of  re- 
semblance to  each  other.  This  latter  statement  is  clearly 
proved  by  the  dillerencc  in  the  result  of  reciprocal  crosses  be- 
tween the  same  two  species,  for,  according  as  the  one  species 
or  the  other  is  used  as  the  father  or  the  mother,  there  is  gen- 
erally some  difieriMice,  and  occasionally  the  widest  possible  dif- 
ference, in  the  facility  of  effecting  a  union.  Tlie  hybrids,  more- 
over, produ(<'d  from  reciprocal  crosses  often  dilTer  in  fertility. 

Now  do  these  complex  and  singular  rules  indicate  that  .spe- 
cies have  b(>en  endowed  with  sterility  simply  to  prevent  their 


244  LAWS  GOVERNING  THE  STERILITY         Chap.  VIIL 

becoming  confounded  in  nature  ?  I  think  not.  For  why 
should  the  sterility  be  so  extremely  difTerent  in  degree,  Avhen 
various  species  are  crossed,  all  of  Avhicli  we  must  suppose  it 
would  l)e  equally  important  to  keej")  from  blending  together? 
Why  should  the  degree  of  sterility  lie  innately  variable  in  the 
individuals  of  the  same  species  ?  Why  should  some  species 
cross  with  facility,  and  yet  produce  very  sterile  hybrids ;  and 
odier  species  cross  with  extreme  dilliculty,  and  yet  produce 
fairly  fertile  hybrids  ?  Why  should  there  often  be  so  great  a 
diflerence  in  the  result  of  a  reciprocal  cross  between  the  same 
two  species  ?  Why,  it  may  even  be  asked,  has  the  production 
of  hybrids  been  permitted  ?  To  grant  to  species  the  special 
power  of  producing  hybrids,  and  then  to  stop  their  further 
l)ro]iagation  by  dilferent  degrees  of  sterility,  not  strictly  related 
to  the  facility  of  the  first  union  between  their  parents,  seems  a 
strange  arrangement. 

The  foregoing  rules  and  facts,  on  the  other  hand,  appear  to 
me  clearly  to  indicate  that  the  sterility  both  of  first  crosses 
and  of  hybrids  is  simplv  incidental  or  dependent  on  unknown 
differences  in  their  reproductive  systems;  the  differences  being 
of  so  peculiar  and  limited  a  nature,  that,  in  reciprocal  crosses 
between  the  same  two  species,  the  male  sexual  element  of  the 
one  will  often  freely  act  on  the  female  sexual  element  of  the 
other,  but  not  in  a  reversed  direction.  It  will  be  advisable  to 
explain  a  little  more  fully  by  an  example  what  I  mean  by  ster- 
ility being  incidental  on  other  differences,  and  not  a  specially- 
endowed  quality.  As  the  capacity  of  one  plant  to  be  grafted 
or  budded  on  another  is  so  unimportant  for  its  Avelfare  in  a 
state  of  nature,  I  prcsmne  that  no  one  will  suppc^se  that  this 
capacity  is  a  specialli/  endowed  quality,  but  will  admit  that  it 
is  incidental  on  differences  in  the  laws  of  growth  of  the  two 
plants.  We  can  sometimes  see  the  reason  why  one  tree  will 
not  take  on  another,  from  differences  in  their  rate  of  growth, 
in  the  hardness  of  their  wood,  in  the  period  of  the  flow  or  na- 
ture of  their  sap,  etc. ;  but  in  a  multitj^de  of  cases  we  can  as- 
sign no  reason  whatever.  Great  diAersity  in  the  size  of  two 
plants,  one  being  Avoody  and  the  other  herbaceous,  one  being 
evergreen  and  the  other  deciduous,  and  adaptation  to  widely- 
different  climates,  do  not  alwaA'S  prevent  the  two  grafting  to- 
gether. As  in  hybridization,  so  with  grafting,  the  capacity  is 
limited  by  systematic  alhniU',  for  no  one  has  been  able  to  graft 
trees  together  belonging  to  ((uite  distinct  families:  and, on  the 
other  hand,   closely-allied   species,  and  varieties  of  the  same 


CiiAi-.  Vin.       OF  FIRST  CROSSPIS   AND   OF  HYBRIDS.  o|5 

species,  can  usually,  but  not  iuvariabl}',  be  grafted  with  case, 
liut  this  capacity,  as  in  hybridization,  is  by  no  means  absolute- 
ly jToverned  by  systematic  allinity.  Althoup^'h  many  distinct 
genera  within  the  same  family  have  been  grafted  together,  in 
otiier  cases  species  of  the  same  genus  will  not  take  on  each 
other.  The  j)ear  can  be  grafted  far  more  readily  on  the 
rpiince,  which  is  ranked  as  a  distinct  genus,  than  on  the  apple, 
wliich  is  a  member  of  the  same  genus.  Even  dilferent  varieties 
of  the  pear  take  with  different  degrees  of  facility  on  the 
quince ;  so  do  dilTerent  varieties  of  the  apricot  and  peach  on 
certain  varieties  of  the  plum. 

As  Gartner  found  that  there  was  sometimes  an  innate  dif- 
ference in  dilferent  individuals  of  the  same  two  species  in 
crossing ;  so  Sageret  behoves  this  to  be  the  case  with  different 
individuals  of  the  same  two  species  in  being  grafted  together. 
As  in  recipi-ocal  crosses,  the  facility  of  effecting  a  union  is 
often  very  far  from  equal,  so  it  sometimes  is  in  grafting;  the 
couimon  gooseberry,  for  instance,  cannot  be  grafted  on  tlie  cur- 
rant, Avhereas  the  currant  will  take,  though  with  difficulty  on 
the  gooseberry. 

AVe  have  seen  that  the  sterility  of  hybrids,  which  have 
their  reproductive  organs  in  an  imperfect  condition,  is  a  differ- 
ent case  from  the  dilHculty  of  uniting  two  pure  species,  which 
have  their  reproductive  organs  perfect ;  yet  these  two  distinct 
cases  run  to  a  certain  extent  parallel.  Something  analogous 
occurs  in  grafting ;  for  Thouin  found  that  three  species  of  llo- 
bini;i,  which  seeded  freely  on  their  own  roots,  and  which  could 
bo  grafted  with  no  great  difficulty  on  another  species,  when 
thus  grafted  were  rendered  barren.  On  the  otiier  hand,  cer- 
tain species  of  Sorbus,  when  grafted  on  other  species,  yielded 
twice  as  much  fruit  as  Avhen  on  their  own  roots.  AVe  are  re- 
minded by  this  latter  fact  of  the  extraordinary  cases  of  Ilip- 
jieastrum,  Passillora,  etc.,  which  seed  much  more  freely  wIkmi 
fertilized  with  the  ])ollen  of  a  distinct  species,  than  wIk.mi  fer- 
tilized with  }K)llen  from  tlie  same  plant. 

Wc  thus  see,  that,  althougli  there  is  a  clear  and  great  dif- 
ference between  the  mere  adhesion  of  grafted  stocks,  and  the 
union  of  the  male  and  female  elements  in  the  act  of  reproduc- 
tion, yet  that  there  is  a  rude  degree  of  parallelism  in  the  re- 
sults of  grafting  and  of  crossing  distinct  species.  And  as  wc 
must  look  at  the  curious  and  complex  laws  governing  the 
facility  with  which  tre(\s  can  be  grafted  on  each  other  as  inci- 
dental  on  unknown  differences  in  their  vegetative  SA'stcms,  so 


246  CAUSES  OF  TIJE  STEUILITY  Cu\r.  VIII. 

I  believe  that  the  still  more  complex  laws  governing!:  the  facili- 
ty of  first  crosses  are  incidental  on  unknown  dillerences  in 
their  reproductive  systems.  These  dilTcrences,  in  both  cases, 
follow  to  a  certain  extent,  as  might  have  been  expected,  sys- 
tematic allinity,  by  Avhieh  every  kind  of  resemblance  and  dis- 
similarity between  organic  beings  is  attempted  to  be  ex- 
jiressed.  The  facts  by  no  means  seem  to  me  to  indicate  that 
the  greater  or  lesser  dilFiculty  of  either  grafting  or  crossing  va- 
rious species  has  been  a  special  endowment ;  although  in  the 
Ciise  of  crossing,  the  difficulty  is  as  important  for  the  endur- 
ance and  stabiUty  of  specific  forms,  as  in  the  case  of  grafting  it 
is  unimportant  for  their  Avelfare. 

Origin  and  Causes  of  the  Ster'tUty  of  First  Crosses  and  of 
JLjbrids. 

At  one  time  it  appeared  to  me  probable,  as  it  has  to  others, 
that  the  sterility  of  iirst  crosses  and  of  hybrids  might  have 
been  slowly  acquired  through  the  natural  selection  of  slightly- 
lessened  degrees  of  fertility,  which  s]iontaneously  appeared, 
like  any  other  variation,  in  certain  indivitluals  of  one  variety 
"when  crossed  with  another  variety.  For  it  would  clearly  be 
advantageous  to  two  varieties  or  incipient  species,  if  they  could 
be  kept  from  blending,  on  the  same  principle  that,  when  man 
is  selecting  at  the  same  time  two  varieties,  it  is  necessary  that 
he  should  keep  them  separate.  In  the  Iirst  place,  it  may  be 
remarked  that  distinct  regions  are  ofteii  inhabited  by  groups 
of  species  and  by  single  species,  which,  when  brought  together 
and  crossed,  are  found  to  be  more  or  less  sterile ;  now  it  could 
clearly  have  been  of  no  advantage  to  such  sejiarated  species  to 
have  been  rendered  mutually  sterile,  and  consequently  this 
could  not  have  been  effected  through  natiu-al  selection ;  but  it 
may  perhaps  be  argued  that,  if  a  species  were  rendered  sterile 
with  some  one  compatriot,  sterility  with  other  species  would 
follow  as  a  necessary  contingency.  In  the  second  place  it  is 
almost  as  much  opposed  to  the  theory  of  natural  selection  as 
to  that  of  special  creation,  that  in  reciprocal  crosses  the  male 
element  of  one  form  should  be  rendered  utterly  impotent  on  a 
second  form,  Avhile  at  the  same  time  the  male  element  of  this 
second  form  is  enabled  freely  to  fertilize  the  Iirst  form  ;  for  this 
peculiar  state  of  the  reproductive  system  could  not  possibly  be 
advantageous  to  either  species. 

In  considering  the  probability  of  natiual  selection  having 


CuAr.  VIII.        OF  FIRST  CROSSES   AND   OF   IIYBKIDS.  247 

come  into  action,  in  rendering  species  mutually  sterile,  one 
frrcat  clifTiculty  will  he  found  to  lie  in  the  existence  of  many 
graduated  steps  from  slin^litly-lesscned  fertility  to  absolute 
sterility.  It  may  be  admitted,  on  the  principle  above  ex- 
plained, that  it  would  \n-oi\t  an  incipient  species  if  it  were 
rendered  in  some  slight  degree  sterile  when  crossed  with  its 
j)ar(>nt-form  or  with  some  other  variety ;  for  thus  fewer  bas- 
tartUzed  and  deteriorated  odspiing  would  be  produced  to  com- 
mingle their  blood  with  the  new  species  in  jirocess  of  forma- 
tion. But  he  who  will  take  the  trouble  to  rellcct  on  the  steps 
by  which  this  first  degree  of  steriUty  could  be  increased  through 
natural  selection  to  that  high  degree  which  is  common  with  so 
many  species,  and  which  is  iniiversol  with  species  which  have 
been  diflerentiated  to  a  generic  or  family  rank,  will  find  the 
subject  extraordinarily  complex.  After  mature  rellection  it 
seems  to  me  that  this  could  not  have  been  effected  through 
natural  selection ;  for  it  could  have  been  of  no  direct  advantiigc 
to  an  individual  animal  to  breed  badly  with  another  indi\-idual 
of  a  dilVcrent  variety,  and  thus  to  leave  few  offspring ;  conse- 
quently such  individuals  could  not  have  been  preserved  or  se- 
lected. Or  take  the  case  of  two  species  which,  in  their  present 
state  when  crossed,  produce  few  and  sterile  oflspring ;  now, 
what  is  there  which  coidd  favor  the  survival  of  those  individuals 
which  ha})pe!ied  to  be  endowed  in  slightly-higher  degree  Avith 
nnitual  infertility,  and  which  thus  approached  by  one  small  step 
toward  absolute  sterility  ?  Yet  an  advance  of  this  kind,  if  the 
theory  of  natural  selection  be  brought  to  bear,  must  have  in- 
cessantly occurred  with  many  species,  for  a  multitude  are  mutu- 
ally quite  barren.  With  sterile  neuter  insects  we  have  reason 
to  believe  that  modifications  in  their  structure  and  fertility  have 
been  slowly  accumulated  by  natural  selection,  from  an  advan- 
tage having  been  thus  indirectly  given  to  the  conununity  to 
which  they  belonged  over  other  communities  of  the  same  spe- 
cies ;  but  an  individual  animal  not  belonging  to  a  social  com- 
numity,  if  rendered  slightly  sterile  when  crossed  with  some 
other  variety,  would  not  thus  itself  gain  any  advantage  or  in- 
directly give  any  advantage  to  the  other  individnals  of  the 
same  variety,  thus  leading  to  their  preservation.  From  these 
considerations  I  infer,  as  far  as  animals  are  concerncil,  that  the 
various  degrees  of  lessened  fertility  which  occur  with  species 
when  crossed  cannot  have  been  slowly  accumulated  by  means 
of  natural  s(>l(>ction. 

With  plants,  it  is  possible  that  the  case  may  be  somewhat 


248  CAUSES  OF  THE  STERILITY  Chap.  VIII. 

(lifTcront.  With  many  kinds,  insects  constantly  ciirry  pollen 
from  neigliboriniT  plants  to  the  stif^mas  of  each  flower ;  and 
"with  some  species  this  is  effected  by  the  •wind.  Now,  if  the 
pollen  of  a  variet}',  when  deposited  on  the  stij]^ia  of  the  same  va- 
riety, should  become  by  spontaneous  variation  in  ever  so  slig'ht  a 
degree  prepotent  over  the  pollen  of  other  varieties,  this  would 
certainly  be  an  advantage  to  the  variety ;  for  its  own  pollen 
would  thus  obliterate  the  efl\3cts  of  the  pollen  of  other  varieties, 
and  prevent  deterioration  of  character.  And  the  more  pre- 
])(^tcnt  the  variety's  own  pollen  could  be  rendered  through  nat- 
ural selection,  the  greater  the  advantage  would  be.  We  know 
from  the  researches  of  Giirtncr  that,  with  s^xjcies  which  are 
mutually  sterile,  the  pollen  of  each  is  always  prepotent  on  its 
own  stigma  over  that  of  the  other  species ;  but  we  do  not 
know  whether  this  prepotency  is  a  consequence  of  the  mutual 
sterility,  or  the  sterility  a  consequence  of  the  prepotency.  If 
the  latter  view  be  correct,  as  the  prepotency  became  stronger 
through  natural  selection,  from  being  advantageous  to  a  spe- 
cies in  process  of  formation,  so  the  sterility  consequent  on  pre- 
potency would  at  the  same  time  be  augmented;  and  the  final 
result  would  be  various  degrees  of  sterility,  such  as  occurs  with 
existing  species.  This  view  might  be  extended  to  animals,  if 
the  female  before  each  birth  received  several  males,  so  that  the 
sexual  element  of  the  prepotent  male  of  her  own  variety  ob- 
literated the  effects  of  the  access  of  previous  males  belonging 
to  other  varieties,  but  we  have  no  reason  to  believe,  at  least 
with  terrestrial  animals,  that  this  is  the  case ;  as  most  males 
and  females  pair  for  each  birth,  and  some  few  for  life. 

On  the  whole  we  may  conclude,  that  with  animals  the  ster- 
ility of  crossed  species  has  not  been  slowly  augmented,  through 
natural  selection  ;  and  as  this  sterility  follows  the  same  general 
laws  in  the  vegetable  as  in  the  animal  kingdom,  it  is  improba- 
ble, though  apparently  possible,  that  with  plants  crossed  spe- 
cies should  have  been  rendered  sterile  by  a  different  process. 
From  this  consideration,  and  remembering  that  species  Avhich 
have  never  coexisted  in  the  same  countiy,  and  Avhich  therefore 
could  not  have  received  any  advantage  from  having  been  ren- 
dei'ed  mutually  infertile,  yet  are  generally  sterile  when  cix)ssed  ; 
and  bearing  in  mind  that  in  reciprocal  crosses  between  the 
same  two  species  there  is  sometimes  the  widest  difference  in 
their  sterility,  we  must  give  up  the  belief  that  natural  selection 
has  come  into  play.  We  are  thus  driven  to  our  former  prop- 
osition, namely,  that   the  sterility  of  first   crosses,  and  indi- 


Chap.  VIII.        UF   FIRST  CROSSES  AND   OF  HYBRIDS.  249 

rcctly  of  hybrids,  is  simply  incidental  on  unknow  n  ditFcrcnccs 
in  tli(^  reproductive  sx'slems  of  the  parent-species. 

We  may  now  try  and  look  a  little  closer  at  tlic  probable 
nature  of  these  dilVerenies,  Avhicli  induce  sterility  in  first  crosses 
and  in  hybrids.  I*iire  species  and  hybrids  difl'er,  as  already  re- 
marked, in  the  state  of  their  reproductive  or<z;ans ;  but  from 
what  Avill  presently  follow  on  reciprocally  dimorphic  and  tri- 
inorphic  plants,  it  would  ajipear  as  if  some  unknown  bond  or 
law  existed,  which  causes  the  young  from  a  union  not  fully 
fertile  to  be  themselves  more  or  less  infertile. 

In  the  case  of  first  crosses  between  pure  species,  the  greater 
or  less  difiiculty  in  eflecting  a  union  antl  in  obtaining  offspring 
aj^parently  depends  on  several  distinct  causes.  There  must 
sometimes  be  a  ])hysical  impossibilit}^  in  the  male  element  reach- 
ing the  ovule,  as  would  be  the  case  with  a  plant  having  a  pistil 
too  long  for  tlie  pollen-tubes  to  reach  the  ovarium.  It  has  also 
been  observed  that  when  pollen  of  one  species  is  placed  on  the 
stigma  of  a  distantly-allied  species,  though  the  pollen-tubes 
protrude,  they  do  not  penetrate  the  stigmatic  surface.  Again, 
the  male  element  may  reach  the  female  element,  but  be  inca- 
pable of  causing  an  embryo  to  be  developed,  as  seems  to  have 
been  the  case  with  some  of  Thuret's  experiments  on  Fuci.  No 
explanation  can  be  given  of  these  facts,  any  more  than  why 
certain  trees  caimot  be  grafted  on  others.  Lastly,  an  embryo 
may  be  developed,  and  then  perish  at  an  early  jieriod.  This 
latter  alternative  has  not  been  sufHciently  attended  to  ;  but  I 
believe,  fj-om  observations  communicated  to  me  by  Mr.  Hewitt, 
who  has  had  great  exjierience  in  hybridizing  pheasants  and 
fowls,  that  the  early  death  of  the  emliryo  is  a  very  frequent 
cause  of  sterility  in  first  crosses.  Mr.  Salter  has  recently  given 
the  results  of  an  examination  of  about  500  eggs  produced  from 
various  crosses  b(itween  three  species  of  Gallus  and  their  hy- 
brids; the  majority  of  these  eggs  had  been  fertilized;  and  in 
the  majority  of  the  fertilized  eggs,  the  embryos  either  had  been 
partially  develojK'd  and  had  then  aborted,  or  had  become  nearly 
mature,  but  the  young  chickens  had  been  imable  to  break 
through  the  shell.  Of  the  chickens  which  were  born,  more  than 
four-fifths  died  within  the  first  few  days,  or  at  latest  weeks, "  with- 
out any  obvious  cause,  apparently  from  mere  inability  to  live;" 
so  that  from  the  oOO  eggs  only  twelve  chickens  were  reared. 
The  early  death  of  hybrid  embryos  jiroliably  occurs  in  like 
manner  Avith  plants;  at  least  it  is  known  that  hybrids  raised 
from  very  distinct  species  arc  sometimes  weak  and  dwarfed, 


250  CAUSES  OF  THE  STERILITY  Ciixr.  VIII 

and  perish  at  an  early  aa;o ;  of  ■vvliicli  fact  Max  Wirliura  has 
recently  given  some  striking'  cases  with  hybrid  -willows.  It 
may  be  here  worth  noticing  that  in  some  cases  of  partheno- 
genesis, embryos  jiroduccd  from  the  eggs  of  silk-motlis,  which 
liad  not  been  fertilized,  passed  through  their  early  stages  of 
development  and  then  perished  like  the  embryos  produced  by 
a  cross  between  two  distinct  species.  Until  becoming  ac- 
quainted with  these  facts,  I  was  unwilling  to  believe  in  the  fre- 
fjuent  early  death  of  hybrid  embryos ;  for  hj-brids,  wlien  once 
born,  are  generally  healthy  and  long-lived,  as  we  see  in  the 
case  of  the  common  mule.  Hybrids,  liowever,  are  differently 
circumstanced  before  and  after  birth  :  when  born  and  living  in 
a  country  where  their  two  parents  live,  they  are  generally 
placed  under  suitable  conditions  of  life.  But  a  hj-brid  partakes 
of  only  half  of  the  nature  and  constitution  of  its  mother,  and 
therefore  before  birth,  as  long  as  it  is  nourished  within  its 
mother's  womb,  or  within  the  egg  or  seed  produced  by  the 
mother,  it  may  be  exposed  to  conditions  in  some  degree  unsuit- 
able, and  consequently  be  liable  to  perish  at  an  early  period; 
more  especially  as  all  very  3-oung  beings  are  eminently  sensitive 
to  injurious  or  uTuiatural  conditions  of  life.  But,  after  all,  the 
cause  more  jirobal)!}'  lies  in  some  imperfection  in  the  original 
act  of  impregnation,  causing  the  embryo  to  be  imperfectly 
developed,  rather  than  in  the  conditions  to  which  it  is  subse- 
quently exposed. 

In  regard  to  the  sterility  of  hyl)rids,  in  whicli  the  sexual  ele- 
ments are  imperfectly  dcveloi)cd,  the  case  is  dilferent.  I  have 
more  than  once  alluded  to  a  large  body  of  facts,  which  I  have 
collected,  showing  that,  when  animals  and  plants  are  removed 
from  tlieir  natin-al  conditions,  they  are  extremely  liable  to  have 
their  reproductive  svstems  seriously  affected.  This,  in  fact,  is 
the  great  bar  to  the  domestication  of  animals.  Between  the 
sterility  thus  sujicrinduced  and  that  of  hybrids,  there  are  many 
points  of  similarity.  In  both  cases  the  sterility  is  independent 
of  general  health,  and  is  often  accompanied  by  excess  of  size 
or  great  luxuriance.  In  both  cases  the  sterility  occurs  in  vari- 
ous degrees ;  in  both,  the  male  element  is  the  most  liable  to 
be  affected  ;  but  sometimes  the  female  more  than  the  male.  In 
both,  the  tendency  goes  to  a  certain  extent  with  S3-stematic 
affinity,  for  whole  groups  of  animals  and  jilants  are  rendered 
impotent  by  the  same  unnatural  conditions;  and  whole  groups 
of  species  lend  to  produce  sterik^  hvbrids.  On  the  other  hand, 
one  species  in  a  grouji  will  sometimes  resist  great  changes  of 


Chap.  VIII.         OF  FIRST  CROSSES   AND   OF  HYBRIDS.  251 

conditions  with  unimpaired  fertility;  and  certain  species  in  a 
p^roiip  will  produce  unusually  fertile  hybrids.  No  one  can  tell, 
till  he  tries,  whether  any  particular  animal  will  breed  under 
confinement,  or  any  exotic  plant  seed  freely  under  culture  ;  nor 
can  he  tell,  till  he  tries,  whether  any  two  species  of  a  genus 
will  produce  more  or  less  sterile  hybrids.  Lastl}^  when  organic 
beings  are  placed  during  several  generations  under  conditions 
not  natural  to  them,  they  are  extremely  liable  to  vary,  which 
seems  to  be  partly  due  to  their  reproductive  systems  having 
been  specially  affected,  though  in  a  lesser  degree  than  when 
sterility  ensues.  So  it  is  with  hybrids,  for  their  offspring  in 
successive  generations  arc  eminently  liable  to  vary,  as  every 
experimentalist  has  observed. 

Thus  we  s(>e  that  when  organic  beings  are  placed  under  new 
and  unnatural  conditions,  and  when  hybrids  are  produced  by 
the  unnatural  crossing  of  two  species,  the  reproductive  system, 
independently  of  the  general  state  of  health,  is  affected  by 
sterility  in  a  very  similar  manner.  In  the  one  case,  tlie  condi- 
tions of  life  have  been  disturbed,  though  ofteit  in  so  slight  a 
degree  as  to  be  inappreciable  by  vis ;  in  the  other  case,  or  that 
of  hybrids,  the  external  conditions  have  remained  the  same, 
but  the  organization  has  been  disturbed  by  two  different  struct- 
ures and  constitutions  having  been  blended  into  one.  For  it 
is  scarcely  possible  that  two  organizations  should  be  com- 
pounded into  one,  without  some  disturbance  occurring  in  the  de- 
velopment, or  periodical  action,  or  mutual  relations  of  the  differ- 
ent parts  and  organs  one  to  another  or  to  the  conditions  of  life. 
When  hyl)rids  are  able  to  breed  inter  se,  they  transmit  to  their 
offsj)ring  from  generation  to  generation  the  same  compounded 
organization,  and  hence  we  need  not  be  surprised  that  their 
sterility,  thougli  in  some  degree  variable,  does  not  diminish;  it 
is  even  a]it  to  increase,  this  being  generally  the  result,  as  l)eforc 
explained,  of  too  close  interbreeding.  The  above  view  of  the 
sterility  of  hybrids  being  caused  by  two  different  constitutions 
being  conlounded  into  one,  has  lately  been  strongly  maintained 
l)y  Max  Wichura  ;  but  it  must  be  owned  that  the  sterility  (as 
will  be  immediately  ex])lained)  which  affects  the  offspring  of 
dimorphic  and  trimorpliic  plants,  when  individuals  l)elonging 
to  the  same  form  are  united,  makes  this  view  rather  doulitful. 
It  should,  however,  be  borne  in  mind  that  the  sterilitv  of  these 
plants  has  been  acfpiired  for  a  special  purpose,  and  may  differ 
in  origin  from  that  of  hybrids. 

It  must  be  owned  that  we  cannot  understand,  on  the  above 


252  STERILITY   OF  HYBRIDS.  Chap.  VIII. 

or  any  other  view,  scvenil  facts  with  respect  to  the  sterility  of 
hybrids  ;  for  instance,  the  unequal  fertility  of  hybrids  produced 
from  reciprocal  crosses;  or  the  increased  sterility  in  those  hy- 
brids Avhich  occasionally  and  exceptionally  reseniljle  closely 
cither  pure  parent.  Nor  do  I  pretend  that  the  foroi^oing  re- 
marks go  to  the  root  of  the  matter ;  no  explanation  is  oflered 
why  an  organism,  when  placed  under  unnatural  conditions,  is 
rendered  sterile.  All  that  I  have  attempted  to  show  is,  that 
in  two  cases,  in  some  respects  allied,  sterility  is  the  common 
result — in  the  one  case  from  the  conditions  of  life  having  been 
disturljed,  in  the  other  case  from  the  organization  or  constitu- 
tion having  been  disturbed  by  two  organizations  being  com- 
pounded into  one. 

A  similar  parallelism  apparently  extends  to  an  allied  yet 
very  different  class  of  facts.  It  is  an  old  and  almost  universal 
belief,  founded  on  a  considerable  body  of  evidence,  that  slight 
changes  in  the  conditions  of  life  are  beneficial  to  all  living 
things.  We  sec  this  acted  on  by  fiirmcrs  and  gardeners  in 
their  frequent  exchanges  of  seed,  tubers,  etc.,  from  one  soil  or 
climate  to  another,  and  back  again.  During  the  convalescence 
of  animals,  great  benefit  is  derived  from  almost  any  cliange  in 
the  habits  of  life.  Again,  both  with  plants  and  animals,  there 
is  abundant  evidence  that  a  cross  between  indiWduals  of  the 
same  species,  which  difltr  to  a  certain  extent,  gives  vigor  and 
fertility  to  the  oflspring;  and  that  close  interbreeding  con- 
tinued during  several  generations  between  the  nearest  rela- 
tions, especially  if  these  be  kept  under  the  same  conditions  of 
life,  almost  always  induces  weakness  and  sterility. 

Hence  it  seems  that,  on  the  one  hand,  slight  clianges  in  the 
conditions  of  life  benefit  all  organic  beings,  and,  on  the  other 
hand,  that  slight  crosses,  that  is,  crosses  between  the  males  and 
females  of  the  same  species,  which  have  varied  and  become 
slightly  different,  give  vigor  and  fertility  to  the  offspring.  But 
we  have  seen  that  greater  changes,  or  changes  of  a  jiarticular 
nature,  often  render  organic  beings  in  some  degree  sterile ; 
and  that  greater  crosses,  tliat  is,  crosses  between  males  and 
females  which  have  become  widely  or  specifically  different, 
produce  hybrids  which  are  generally  sterile  in  some  degree. 
I  cannot  persuade  myself  that  this  parallelism  is  an  accident 
or  an  illusion.  Both  series  of  facts  seem  to  be  connected  to- 
gether by  some  common  but  unknown  bond,  which  is  essen- 
tially related  to  the  principle  of  life  ;  this  principle  apparently 
being  that  life,  as  Mr.  Herbert  Spencer  has  remarked,  depends 


Chap.  VIII.  DIMORPHISM  AND   TRIMOKPIllSM.  253 

on,  or  consists  in,  the  incessant  action  and  reaction  of  various 
forces,  which,  as  throui^liout  Nature,  are  always  tending  toward 
an  e(iuilihriuiii ;  and  when  this  tendency  is  slip^htly  disturbed 
by  any  change,  tlie  vital  forces  apparently  gain  in  power. 

Meciprocal  Dimorphism  and  Trimorpliism. 

This  subject  may  he  here  briefly  discussed,  and  will  l)e 
found  to  throw  some  light  on  hybridism.  Several  plants  belong- 
ing to  distinct  orders  present  two  forms,  which  exist  in  al)out 
equal  numbers,  and  whicli  differ  in  no  respect  except  in  tlieir 
re])roductive  organs  ;  one  form  having  a  long  pistil  with  short 
stamens,  tlie  other  a  short  ])istil  with  long  stamens;  botli  with 
dilVerently-sized  pollen-grains.  With  trimorphic  plants  there 
are  three  forms  likewise  difl'ering  in  the  lengths  of  their  pistils 
and  stamens,  in  the  size  and  color  of  the  pollen-grains,  and  in 
some  otlier  respects ;  and  as  in  each  of  the  three  forms  there 
are  two  sets  of  stamens,  there  arc  altogether  six  sets  of  stamens, 
and  three  kinds  of  pistils.  These  organs  are  so  proportioned 
in  length  to  each  other,  that,  in  any  two  of  the  forms,  half  the 
stamens  in  each  stand  on  a  level  with  the  stigma  of  the  third 
fonn.  Now  I  have  shown,  and  the  result  has  been  confirmed 
Ijy  other  observers,  that,  in  order  to  obtain  full  fertility  Avith 
these  ])lants,  it  is  necessary  that  the  stigma  of  the  one  form 
should  be  fertilized  by  pollen  taken  from  the  stamens  of  corre- 
sponding height  in  the  other  form.  So  that  with  dimorphic 
species  two  unions,  wliich  may  be  called  legitimate,  arc  fully 
fertile ;  and  two,  which  may  be  called  illegitimate,  are  more 
or  less  infertile.  AVith  tnmorj>hic  species  six  imions  are  legiti- 
mate or  fully  fertile,  and  twelve  are  illegitimate  or  more  or 
less  infertile. 

The  infertility  which  may  be  observed  in  various  dimorphic 
and  trimorphic  ])lants,  when  they  are  illegitimately  fertilized, 
that  is,  by  ]io]Um)  taken  from  stamens  not  coi'responding  in 
height  villi  the  pistil,  dilTers  much  in  degree,  up  to  absolute 
and  utter  sttM-ility  ;  just  in  the  same  manner  as  occurs  in  cross- 
ing distinct  species.  As  the  degree  of  sterility  in  the  latter 
case  depends  in  an  eminent  degree  on  the  conditions  of  life 
being  more  or  less  favorable,  so  I  have  found  it  witli  iUegitimate 
imions.  It  is  well  known  that  if  pollen  of  a  distinct  species 
be  placed  on  the  stigma  of  a  flower,  and  its  own  ]iollen  be 
afterward,  even  after  a  considerable  interval  of  time,  placed  on 
the  same  stigma,  its  action  is  so  strongly  prepotent  that   it 


g.54  RECIPKOCAL  DIMORPHISM  Cuap.  VIII. 

generally  amiiliilatcs  the  effect  of  the  foreign  pollen;  so  it  is 
with  the  pollen  of  the  several  forms  of  the  same  species,  for 
legitimate  pollen  is  strongly  prepotent  over  illegitimate  pollen, 
when  botii  are  placed  on  the  same  stigma.  I  ascertained  this 
by  fertilizing  several  flowers,  first  illegitimately  and  twenty- 
four  hours  afterward  legitimately,  with  pollen  taken  from  a 
peculiarly-colored  variety,  and  all  the  seedlings  were  similarly 
colored;  this  shows  that  the  legitimate  pollen,  though  applied 
twenty-four  hours  subsequently,  had  wholly  destroyed  or  pre- 
vented the  action  of  the  previously-applied  illegitimate  pollen. 
Again,  as  in  making  reciprocal  crosses  between  the  same  two 
species,  there  is  occasionally  a  great  difference  in  the  result,  so 
the  same  thing  occurs  Avith  trimorphic  plants ;  for  instance, 
the  mid-styled  form  of  Lythrum  salicaria  Avas  illegitimately 
fertilized  with  the  greatest  case  by  pollen  from  the  longer  sta- 
mens of  the  short-styled  form,  and  yielded  many  seeds ;  but 
the  latter  form  did  not  yield  a  single  seed  when  fertilized  by 
the  longer  stamens  of  the  mid-styled  form. 

In  all  these  respects  and  in  others  which  might  have  been 
adduced,  the  forms  of  the  same  imdoubted  species  when  ille- 
gitimately united  behave  in  exactly  the  same  manner  as  do  two 
distinct  S[)ecics  wheii  crossed.  This  led  me  carefully  to  ob- 
serve during  four  years  many  seedlings,  raised  from  several 
illegitimate  unions.  The  chief  result  is  that  these  illegitimate 
])lants,  as  they  may  be  called,  are  not  fully  fertile.  It  is  possi- 
ble to  raise  from  dimorphic  species  both  long-styled  and  short- 
styled  illegitimate  plants,  and  from  trimorphic  plants  all  three 
illegitimate  forms  ;  these  can  then  be  properly  united  in  a  le- 
gitimate maimer.  When  this  is  done,  there  is  no  apparent 
reason  why  they  should  not  yield  as  many  seeds  as  did  their 
parents  when  legitimately  fertilized.  But  such  is  not  the  case  ; 
they  are  all  infertile,  but  in  various  degrees;  some  being  so 
utterly  and  incurably  sterile  that  they  did  not  yield  during 
four  seasons  a  single  seed  or  even  seed-capsule.  The  sterility 
of  these  illegitimate  plants,  when  united  with  each  other  in  a 
legitimate  manner,  may  be  strictly  compared  with  that  of  hy- 
brids when  crossed  inter  sc.  When  on  the  other*  hand  a  hybrid 
is  crossed  with  either  pure  parent-species,  the  sterility  is  usu- 
ally much  lessened :  and  so  it  is  when  an  illegitimate  plant  is 
fertilized  by  a  legitimate  plant.  In  the  same  manner  as  the 
sterility  of  hybrids  does  not  always  run  parallel  with  the  difii- 
culty  of  making  the  first  cross  between  the  two  j^arent-species, 
so  the  sterility  of  certain  illegitimate  plants  was  usually  great, 


f'liAr.  VIII.  AND   TRIMORPIIISM.  205 

while  tlic  sterility  of  the  union  from  which  they  were  derived 
was  hy  no  means  f^n\it.  ^Vith  liybrids  raised  from  the  same 
seed-capsule  the  deforce  of  sterility  is  innately  variable,  so  it 
is  in  a  marked  manner  with  illefritimate  plants.  Lastly,  many 
hybrids  arc  profuse  and  persistent  flowcrers,  while  other  and 
more  sterile  hybrids  produce  few  flowers,  and  arc  weak,  miser- 
able dwarfs  ;  exactly  similar  cases  occur  with  the  illegitimate 
oflspring  of  various  dimordhic  and  trimorphic  plants. 

Altogether  there  is  the  closest  identity  in  character  and  be- 
havior between  illegitimate  plants  and  hybrids.  It  is  hardly 
an  exaggeration  to  maintain  that  the  former  are  hybrids,  but 
jjroduced  within  the  limits  of  the  same  species  by  the  imjiroper 
imion  of  certain  forms,  while  ordinary  hybrids  are  produced 
from  an  improper  union  between  so-called  distinct  species. 
We  have  also  already  seen  that  there  is  the  closest  similarity  in 
all  respects  between  first  illegitimate  unions  and  first  crosses 
l)e+wcen  distinct  species.  This  will  perhaps  be  made  more 
fully  ajiparcnt  by  an  illustration  :  we  may  suppose  that  a  bot- 
anist found  two  well-marked  varieties  (and  such  occur)  of  the 
loiig-stjled  form  of  the  trimorphic  Lythrum  salicaria,  and  that 
he  determined  to  try  by  crossing  whether  they  Mere  specifi- 
cally distinct.  He  would  find  that  they  yielded  only  about  one- 
fifth  of  the  proper  number  of  seed,  and  that  they  behaved  in  all 
the  other  above-specified  respects  as  if  they  had  been  two  dis- 
tinct species.  But  to  make  the  case  sure,  he  would  raise  plants 
from  his  supposed  hybridized  seed,  and  he  would  find  that  the 
seedlings  were  miserably  dwarfed  and  utterly  sterile,  and  that 
they  behaved  in  all  other  respects  like  ordinary  hybrids.  He 
might  then  maintain  that  he  had  actually  proved,  in  accordance 
with  the  common  view,  that  his  two  varieties  were  as  good 
and  as  distinct  species  as  any  in  the  world ;  but  he  would  be 
completely  mistaken. 

The  facts  now  given  on  dimorphic  and  trimorphic  plants 
an»  important,  because  they  show  us,  first,  that  the  ])hysi()logi- 
cal  test  of  lessened  fertility,  both  in  first  crosses  and  in  hyl)ri(ls, 
is  no  safe  critericm  of  specific  distinction  ;  secondly,  because  we 
may  conclude  that  there  is  some  unknown  bond  which  connects 
(li(>  infertility  of  illegitimate  unions  with  that  of  their  illegiti- 
mate oflspring,  and  we  an*  led  to  extend  the  same  view  to  lirst 
crosses  and  hybrids  ;  thirdly,  because  we  find,  and  this  seems 
to  me  of  especial  importance,  that  two  or  three  forms  of  the 
same  species  may  exist  and  may  differ  in  no  respect,  except  in 
their  reproductive  organs,  and  yet  be  sterile  when  united  in 


256  FERTILITY   OF   VARIETIES  Chap.  VIII. 

certain  -ways.  With  dimorpliic  plants,  tlie  unions  between  the 
two  distinct  forms  arc  alone  quite  fertile,  and  jmxluce  quite 
fertile  ofl'spring-,  while  unions  between  individuals  belonging 
to  the  same  form  are  more  or  less  sterile ;  so  that  the  result  is 
exactly  the  reverse  of  what  occurs  with  distinct  sj)ecies.  With 
dimorphic  plants  the  resultant  sterility  is  quite  indejiendent  of 
any  difference  in  general  structure  or  constitution,  for  it  arises 
from  the  union  of  individuals  belonging  not  only  to  the  same 
species,  but  to  the  same  form.  It  must,  therefore,  depend  on 
the  nature  of  the  sexual  elements,  which  are  so  adapted  to  each 
other,  that  the  male  and  female  elements  occurring  in  the  same 
form  do  not  suit  each  other,  Avhile  those  occurring  in  the  two 
distinct  forms  are  mutually  suited  to  each  other.  From  these 
considerations,  it  seems  proljable  that  the  sterility  of  distinct 
species  when  crossed,  and  of  their  hybrid  progeny,  dejiends  ex- 
clusively on  the  nature  of  their  sexual  elements,  and  not  on 
any  general  difference  in  structure  or  constitution.  We  are, 
indeed,  led  to  this  same  conclusion  by  considering  reciprocal 
crosses,  in  which  the  male  of  one  species  cannot  be  imited,  or 
can  be  imited  with  great  dilhculty,  with  the  female  of  a  sec- 
ond species,  while  the  converse  cross  can  be  effected  with  per- 
fect facility ;  for  this  difference  in  the  facility  of  making  recip- 
rocal crosses  and  in  the  fertility  of  their  offspring  must  be  at- 
tributed cither  to  the  male  or  to  the  female  element  in  the  first 
species  having  been  differentiated,  with  reference  to  the  sexual 
elements  of  the  second  species  in  a  higher  degree  than  in  the 
converse  case.  That  excellent  observer,  Gartner,  likewise 
came  to  this  same  conclusion,  namely,  that  species  when 
crossed  are  sterile  owing  to  differences  confined  to  their  repro- 
ductive systems. 

Fertility   of  Varieties   tchen   crossed,  and  of  their  Mongrel 

Offqyring. 

It  may  be  urged,  as  an  overwhelming  argument,  that  there 
must  be  some  essential  distinction  between  species  and  varie- 
ties, inasmuch  as  the  latter,  however  nuich  tliey  may  differ 
from  each  other  in  external  ajipearance,  cross  with  perfect  facil- 
it>-,  and  yield  perfectly  fertile  offspring.  Witli  some  excep- 
tions, presently  to  be  given,  I  fully  admit  that  this  is  the  rule. 
But  the  subject  is  surrounded  by  difliculties,  for,  looking  to  va- 
rieties, produced  under  nature,  if  two  forms  hitherto  reputed  to 
be  varieties  be  found  in  any  degree  sterile  together,  they  are 


Chap.  VIII.  WHEN  CROSSED.  257 

.it  onre  ranked  l)v  ina.sl  naturalists  as  species.  For  instance, 
the  l)lue  and  red  ijiiiipi'rnel,  wliich  are  considered  by  most  bot- 
anists as  varieties,  are  said  l)y  Giirtncr  not  to  be  quite  fertile 
when  crossed,  and  he  consequently  ranks  them  as  undoubted 
species.  If  we  thus  art»-uo  in  a  circle,  the  fertility  of  all  varie- 
ties produced  under  nature  will  assuredly  have  to  be  granted. 

If  we  turn  to  varieties,  produced,  or  supposed  to  have  been 
j)roduced,  under  domestication,  we  arc  still  involved  in  doubt. 
For  when  it  is  stated,  for  instance,  that  the  German  Spitz  dog 
crosses  more  easily  with  the  fox  than  do  other  dogs,  or  that 
(v-rtain  South  American  indigenous  domestic  dogs  do  not 
rcadilv  unite  with  European  dogs,  the  explanation  which  will 
o^'cur  to  every  one,  and  jirobably  the  true  one,  is,  that  these 
dogs  are  descended  from  aboriginally  distinct  species.  Never- 
theless the  perfect  fertility  of  so  many  domestic  varieties,  dif- 
fering widely  from  each  other  in  appearance,  for  instance  those 
of -the  pigeon,  or  of  the  cabbage,  is  a  remarkable  fact;  more 
especially  when  we  reflect  how  many  species  there  arc,  which, 
though  resembling  each  other  most  closely,  are  utterly  sterile 
wiien  intercrossed.  Several  considerations,  how'ever,  render 
the  fertility  of  domestic  varieties  less  remarkable.  In  the  first 
])hice,  it  may  be  observed  that  the  amount  of  external  dill'er- 
cnce  between  two  species  is  no  suni  guide  to  their  degree  of 
mutual  sterility,  so  that  similar  differences  in  the  case  of  vari- 
eties would  be  no  sure  guide.  It  is  almost  certain  that  with 
species  the  cause  lies  exclusively  in  differences  in  their  sexual 
constitution.  Now  the  conditions  to  which  domesticated  ani- 
mals and  cultivated  plants  have  been  subjected,  have  had  so 
little  tendency  tow^ard  modifying  the  reproductive  system  in  a 
manner  leading  to  mutual  sterility,  that  we  have  good  grounds 
for  admitting  the  directly  opposite  doctrine  of  Pallas,  namely, 
that  such  conditions  generally  eliminate  this  tendency;  so  that 
the  domesticated  descendants  of  species,  which  in  their  natural 
state  would  have  becMi  in  some  degree  sterile  when  crossed, 
become  ])(;rfectly  fertile  together.  With  plants,  so  far  is  cul- 
tivation from  giving  a  tendency  toward  sterility  between  dis- 
tinct species,  that  in  several  well-authenticated  cases  already 
alluded  to,  certain  ])lants  have  been  affected  in  an  opposite 
mann(^r,  for  they^  have  become  self-impotent,  while  still  retain- 
ing the  ea|)a(itv  of  fertilizing  and  being  fertilized  by,  other 
species.  If  the  Pallasian  doctrine  of  the  elimination  of  sterility 
through  long-continued  domestication  be  admitted,  and  it  can 
hardly  be  rejected,  it  becomes  in  the  highest  degree  improl> 


258  FERTILITV   OF  VARIETIES  Chap.  VIII. 

tiblc  tliat  similar  circumstances  should  both  induce  and  elimi- 
nate the  same  tendency ;  though  in  certain  cases,  with  species 
liaving  a  peculiar  constitution,  sterility  might  occasionally  be 
thus  induced.  Tims,  as  I  believe,  we  can  understand  why  with 
domesticated  animals  varieties  have  not  been  produced  which 
arc  mutually  sterile  ;  and  why  with  plants  only  a  few  such 
cases,  immediately  to  l)e  given,  have  been  observed. 

The  real  difficulty  in  our  present  subject  is  not,  as  it  ap- 
pears to  me,  why  domestic  varieties  have  not  become  mutually 
infertile  when  crossed,  but  why  this  has  so  generally  occun-ed 
Avith  natural  varieties  as  soon  as  they  have  been  modified  in  a 
sufficient  and  permanent  degree  to  take  rank  as  species.  "We 
are  far  from  precisely  knowing  the  cause ;  nor  is  this  surpris- 
ing, seeing  hovv'  profoundly  ignorant  we  are  in  regard  to  the 
normal  action  of  the  reproductive  system.  But  we  can  see  that 
species,  owing  to  their  struggle  for  existence  with  numerous 
competitors,  must  have  been  exposed  to  more  uniform  condi- 
tions during  long  periods  of  time,  than  have  been  domestic 
varieties ;  and  this  may  well  make  a  wide  difference  in  the  re- 
sult. For  we  know  how  commonly  wild  animals  and  plants, 
when  taken  from  their  natural  conditions  and  subjected  to  cap- 
tivity, are  rendered  sterile ;  and  the  reproductive  functions  of 
organic  beings,  which  have  always  lived  and  been  slowly  mod- 
ilied  under  natural  conditions,  would  probably  in  like  manner 
be  eminently  sensitive  to  the  influence  of  an  unnatural  cross. 
Domesticated  productions,  on  the  other  hand,  which,  as  shown 
by  the  mere  fact  of  their  domestication,  were  not  originally 
highly  sensitive  to  changes  in  their  conditions  of  life,  and 
winch  can  now  generally  resist  with  undiminished  fertility 
repeated  changes  of  conditions,  might  be  expected  to  produce 
varieties,  Avhich  would  be  little  liable  to  have  their  reproduc- 
tive powers  injuriously  affected  by  the  act  of  crossing  with 
other  varieties  which  had  originated  in  a  like  manner. 

I  have  as  yet  spoken  as  if  the  varieties  of  the  same  species 
were  invariably  fertile  when  intercrossed.  But  it  is  impossible 
to  resist  the  evidence  of  the  existence  of  a  certain  amount  of 
sterility  in  the  few  following  cases,  which  I  will  briefly  abstract. 
Tiie  evidence  is  at  least  as  good  as  that  from  which  we  believe 
in  the  sterility  of  a  multitude  of  s]iecies.  The  evidence  is,  also, 
derived  from  hostile  Avitncsses,  who  in  all  other  cases  consider 
fertility  and  sterility  as  safe  critej-ions  of  specific  distinction. 
Giirtner  kept  during  several  years  a  dwarf  kind  of  maize  with 
yellow  seeds,  and  a  tall  variety  with  red  seeds  growing  ncai 


Chap.  VIII.  WHEN  CROSSED.  059 

each  oilier  in  his  r.arclcn  ;  and  although  these  j)lants  liavc 
separated  sexes,  they  never  naturally  crossed.  lie  then  fertil- 
ized thirteen  flowers  of  the  one  with  the  pollen  of  the  other; 
but  only  a  sing-le  head  jiroduced  any  seed,  and  this  one  head 
produced  onl}'  live  j^rains.  Manipulation  in  this  case  could  not 
have  l)een  injurious,  as  the  plants  have  separated  sexes.  No 
one,  I  believe,  has  suspected  that  these  varieties  of  maize  arc 
distinct  species;  and  it  is  important  to  notice  that  the  hybrid 
plants  thus  raised  were  themselves  j^erfecthj  fertile ;  so  that 
even  Gartner  did  not  venture  to  consider  the  two  varieties  as 
specilically  distinct. 

Girou  do  Buzareingues  crossed  three  varieties  of  gourd, 
which,  like  the  maize,  has  separated  sexes,  and  he  asserts  that 
their  mutual  fertilization  is  by  so  much  the  less  easy  as  their 
differences  are  greater.  How  far  these  experiments  may  be 
trusted,  I  know  not ;  but  the  forms  experimented  on  are 
rapked  by  Sageret,  who  mainly  founds  his  classification  by  the 
test  of  infertility,  as  varieties;  and  Naudin  has  come  to  the 
same  conclusion. 

The  following  case  is  far  more  remarkable,  and  seems  at 
fh-st  quite  incredible ;  but  it  is  the  result  of  an  astonishing 
number  of  experiments  made  during  many  years  on  nine  spe- 
cies of  Verbascmn,  by  so  good  an  observer  and  so  hostile  a 
witness  as  Gartner;  namely,  that  the  yellow  and  white  varie- 
ties when  crossed  i)roduce  less  seed  than  the  similarly-colored 
varic;ties  of  the  same  species.  Moreover,  he  asserts  that,  when 
yellow  and  white  varieties  of  one  species  are  crossed  with  yel- 
\o\v  and  white  varieties  of  a  distinct  species,  more  seed  is  pro- 
duced by  the  crosses  between  the  similarly-colored  flowers 
than  between  those  which  are  diflerently  colored.  ]\lr.  Scott, 
also,  has  experimented  on  the  species  and  varieties  of  Verbas- 
cum ;  and,  although  unable  to  ctrnfinn  Gartner's  results  on  the 
crossing  of  the  distinct  species,  he  finds  that  the  dissimilarly- 
colored  varieties  of  the  same  species  yield  fewer  seeds,  in  the 
proportion  of  8G  to  100,  than  the  similarly-colored  varieties, 
^'et  these  varieties  difl'er  in  no  respect,  except  in  the  color  of 
their  flowers;  and  one  variety  can  sometimes  be  raised  from 
the  seed  of  another. 

Kolrcuter,  whose  accuracy  has  been  confirmed  by  every 
subscijucnt  observer,  has  proved  th(»  remarkal)le  fact  that  one 
particular  variety  of  the  connnon  tobacco  was  more  fertile  than 
the  other  variiMies,  when  cro.ssed  with  a  widely-distinct  species. 
He  experimented  on  live  fonns,  which  are  commonly  reputed 


o(;,j  HYBRIDS  AND   MONGRELS   COMPARED.      Chap.  VIII. 

to  be  varieties,  and  which  he  tested  by  the  severest  trial, 
namel}',  by  reciprocal  crosses,  and  he  found  their  mongrel  ofl- 
sprinf^  perfectly  fertile.  But  one  of  these  five  varieties,  when 
used  either  as  the  father  or  mother,  and  crossed  with  the  Nico- 
tiana  glutinosa,  always  yielded  hybrids  not  so  sterile  as  those 
which  were  produced  from  the  four  other  varieties  when  crossed 
with  Nicotiana  glutinosa.  Hence  the  reproductive  system  of 
this  one  variety  must  have  been  in  some  manner  and  in  some 
degree  modified. 

From  these  facts  it  cannot  be  maintained  that  varieties 
when  crossed  are  invariably  (luitc  fertile :  from  the  great  diffi- 
culty of  ascei'taining  the  infertility  of  varieties  in  a  state  of 
nature,  for  a  supposed  variety,  if  proved  to  be  infertile  in  any 
degree,  would  almost  universally  be  ranked  as  a  species ;  from 
man  attending  only  to  external  characters  in  liis  domestic  va- 
rieties, and  from  such  varieties  not  having  been  exposed  for  a 
very  long  period  to  uniform  conditions  of  life.  From  these  sev- 
eral considerations  we  may  conclude  that  fertility  does  not  con- 
stitute a  fundamental  distinction  between  varieties  and  species 
when  crossed.  The  general  sterility  of  crossed  species  may 
safely  be  looked  at  not  as  a  special  acquirement  or  endowment, 
but  as  incidental  on  changes  of  an  vmknown  nature  in  their 
sexual  elements. 

Hybrids  and  3fonr/rels  compared^  independently  of  their 
Fertility. 

Independently  of  the  quest i(m  of  fertility,  the  offspring  of 
species  when  crossed,  and  of  varieties  when  crossed,  may  be 
compared  in  several  other  respects.  Giirtuer,  whose  strong 
wish  it  was  to  draw  a  distinct  line  between  species  and  varie- 
ties, could  find  very  few,  and,  as  it  seems  to  me,  quite  unim- 
portant differences  between  the  so-called  hybrid  offspring  of 
species,  and  the  so-called  mongrel  offspring  of  varieties.  And, 
on  the  other  hand,  they  agree  most  closely  in  many  im2:)ortant 
respects. 

I  shall  here  discuss  this  subject  with  extreme  brevity.  The 
most  important  chstinction  is,  that  in  the  first  generation  mon- 
grels are  more  variable  than  hybrids ;  but  Gartner  admits  that 
hybrids  from  species  which  have  long  been  cultivated  are  often 
variable  in  the  first  generation;  and  1  have  myself  seen  striking 
instances  of  this  fact.  Gartner  further  admits  that  liybrida 
between  very  closely-allied  species  are   more   variable    than 


Cii4.r.  VIII.      IIVIJRIDS   AND  MONGRELS   COMPARED.  ogi 

those  from  very  distinct  species ;  and  this  shows  that  the  dif- 
ference in  the  degree  of  variability  graduates  away.  When 
mongrels  and  the  more  fertile  liybrids  are  propagated  for  sev- 
eral generations,  an  extreme  amount  of  variability  in  the  off- 
spring in  both  cases  is  notorious ;  but  some  few  instances  of 
botli  hybrids  and  mongrels  long  retaining  a  imifonn  character 
could  be  given.  The  variability,  however,  in  the  successive 
generations  of  mongrels  is,  perhaps,  p^eater  than  in  hybrids. 

This  greater  variability  in  mongrels  than  in  hybrids  docs 
not  seem  at  all  surprising.  For  the  parents  of  mongrels  are 
varieties,  and  mostly  domestic  varieties  (very  few  ex])eriments 
having  been  tried  on  natural  varieties),  and  this  imjjlies  that 
there  lias  been  recent  variability,  Avhich  would  often  continue 
and  be  added  to  that  arising  from  the  act  of  crossing.  The 
slight  variability  of  hybrids  in  the  first  generation,  in  contrast 
with  the  succeeding  generations,  is  a  curious  fixct,  and  deserves 
attention.  For  it  bears  on  the  view  which  I  have  taken  of  one 
of  the  causes  of  ordinary  variability ;  namely,  that  the  repro- 
ductive systeni  from  being  eminently  sensitive  to  changed  con- 
ditions of  life,  fails  under  these  circumstances  to  perform  its 
proper  function  of  producing  offspring  identical  in  all  respects 
with  the  parent-form.  Now,  hybrids  in  the  first  generation 
are  descended  from  sjiecies  (excluding  those  long  cultivated) 
which  have  not  had  their  reproductive  systems  in  any  way 
allected,  and  they  are  not  variable  ;  but  hybrids  themselves 
have  their  reproductive  systems  seriously  affected,  and  their 
descendants  are  highly  variable. 

Biit  to  return  to  our  comparison  of  mongrels  and  hybrids : 
Gfirtner  states  that  mongrels  are  more  liable  than  hybrids  to 
revert  to  cither  parent-form ;  but  this,  if  it  be  true,  is  certainly 
only  a  difference  in  degree.  Mort>over,  Gartner  expressly  states 
that  hylirids  from  long-cultivated  plants  are  more  subject  to 
reversion  than  hybrids  from  species  in  their  natural  state;  and 
this  probably  explains  the  singular  difference  in  the  results 
arrived  at  by  dilferent  obser\'ers :  thus,  Max  Wichura  doubts 
whether  hybrids  ever  revert  to  their  parent-forms,  and  he  ex- 
perimented on  uncultivated  species  of  willows  ;  while  Naudin, 
on  the  other  hand,  insists  in  the  strongest  terms  on  the  almost 
universal  tendencv  to  reversion  in  hybrids,  and  he  experiment- 
ed chiedy  on  cultivated  plants.  Gartner  further  stiites  that 
when  any  two  species,  although  most  closely  allied  to  each 
other,  are  crossed  with  a  third  species,  the  hybrids  arc  widely 
different  from  each  other;  Avhereas,  if  two  vtM-y  distinct  varie- 


262  HYBRIDS  AND  MONGRELS  COMPARED.      Chap.  VIII. 

ties  of  one  species  are  crossed  with  another  species,  the  hybrids 
do  not  diiler  much.  But  this  conclusion,  as  far  as  I  can  make 
out,  is  founded  on  a  sinp^le  experiment;  and  seems  directly 
opposed  to  tlie  results  of  several  experiments  made  by  Kol- 
reuter. 

Such  alone  arc  the  imimportant  dilTercnces  which  Gartner 
is  able  to  point  out  between  hybrid  and  moiig'rel  plants.  On 
the  other  hand,  the  dco-recs  and  kinds  of  resemblance  in  mon- 
g^rels  and  in  hybrids  to  their  respective  parents,  more  especially 
in  hybrids  produced  from  nearly  related  species,  follow  accord- 
ing to  Giirtncr  the  same  laws.  When  two  species  are  crossed, 
one  has  sometimes  a  prepotent  power  of  impressing  its  likeness 
on  the  hybrid  ;  and  so  I  believe  it  to  be  with  varieties  of  plants. 
With  animals  one  variety  certainly  often  has  this  prepotent 
power  over  another  variety.  Hybrid  plants  produced  from  a 
reciprocal  cross,  generally  resemble  each  other  closely ;  and  so 
it  is  with  mongrel  plants  from  a  reciprocal  cross.  Both  hybrids 
and  mongrels  can  be  reduced  to  either  pure  parent-form,  by 
repeated  crosses  in  successive  generations  Avith  cither  parent. 

These  several  remarks  are  apparently  applicable  to  animals  ; 
but  the  subject  is  here  much  complicated,  partly  owing  to  the 
existence  of  secondary  sexual  characters  ;  but  more  especially 
owing  to  prepotency  in  transmitting  likeness  running  more 
strongly  in  one  sex  than  in  the  other,  both  when  one  species 
is  crossed  with  another,  and  when  one  variety  is  crossed  with 
another  variety.  For  instance,  I  think  those  authors  are  right, 
Avho  maintain  that  the  ass  has  a  prepotent  power  over  the  horse, 
so  that  botli  the  mule  and  the  hinny  more  resemble  the  ass  than 
tlie  horse  ;  but  that  the  prepotency  runs  more  strongly  in  the 
male-ass  than  in  the  female,  so  that  the  mule,  which  is  the  off- 
spring of  the  male-ass  and  mare,  is  more  like  an  ass,  than  is  the 
hinny,  Avhich  is  the  offspring  of  the  female-ass  and  stallion. 

Much  stress  has  been  laid  by  some  authors  on  the  supposed 
fact,  that  it  is  only  Avith  mongrels  that  the  offspring  are  not 
intermediate  in  character,  but  closely  resemble  one  of  their 
parents ;  but  this  does  sometimes  occur  Avitli  hybrids,  yet  I 
grant  much  less  frequently  Avith  them  than  Avitli  mongrels. 
Looking  to  the  cases  Avliich  I  have  collected  of  cross-bred  ani- 
mals closely  resembling  one  parent,  the  resemblances  seem 
cliiefly  confined  to  characters  almost  monstrous  in  their  nature, 
and  Avhich  have  suddcidy  appeared — such  as  albinism,  melanism, 
deficiency  of  tail  or  horns,  or  additional  fingers  and  toes;  and 
do  not  relate  to  characters  Avhich  have  been  sloAvly  ac(|uired 


Chap.  VIU.  SUMMARY.  263 

through  selection.  Consequently,  sudden  reversions  to  the 
perfect  character  of  either  parent  would  be  much  more  likely 
to  occur  with  mono-rels,  Avhicli  are  descended  from  varieties 
often  sudd(Mily  produced  and  semi-monstrous  in  character,  than 
with  hvbrids,  which  are  descended  from  species  slowly  and 
naturally  produced.  On  the  whole,  I  entirely  agree  witli  Dr. 
Prosper  Lucas,  who,  after  arranging  an  enormous  body  of  facts 
with  respect  to  animals,  comes  to  the  conclusion  that  the  laws 
of  resemblance  of  the  child  to  its  parents  are  the  same,  whether 
the  two  parents  dilTer  little  or  nmch  from  each  other,  namely 
in  the  imion  of  individuals  of  the  same  variety,  or  of  different 
varieties,  or  of  distinct  species. 

Independently  of  the  question  of  fertility  and  sterility,  in 
all  other  respects  there  seems  to  be  a  general  and  close  simi- 
larity in  the  offspring  of  crossed  species,  and  of  crossed  vari- 
eties. If  we  look  at  species  as  having  been  specially  created, 
an'd  at  varieties  as  having  been  produced  by  secondary  laws, 
this  similarity  would  be  an  astonishing  fact.  But  it  harmo- 
nizes perfectly  with  the  view  that  there  is  no  essential  dis- 
tinction l^etwcen  species  and  varieties. 

Summary  of  Chapter. 

First  crosses  between  forms  sufficiently  distinct  to  be  ranked 
as  species,  and  their  hybrids,  are  very  generally  but  not  univer- 
sally sterile.  The  sterility  is  of  all  degrees,  and  is  often  so 
slight  that  the  most  careful  experimentalists  have  arrived  at 
diametrically  ojiposite  conclusions  in  ranking  forms  by  this 
test.  The  sterility  is  innately  variable  in  individuals  of  the 
same  species,  and  is  eminently  susceptible  to  the  action  of 
favorable  and  imfavorable  conditions.  The  degree  of  sterility 
does  not  strictly  follow  systematic  affinity,  but  is  governed  by 
several  curious  and  complex  laws.  It  is  generally  different, 
and  sometimes  widely  different,  in  reciprocal  crosses  between 
tlie  same  two  species.  It  is  not  always  equal  in  degree  in  a 
first  cross  and  in  the  hybrids  produced  from  this  cross. 

In  the  same  manner  as  in  grafting  trees,  the  capacity  of  one 
species  or  variety  to  take  on  another,  is  incidental  on  differ- 
ences, generally  of  an  unknown  nature,  in  their  vegetative  sys- 
tems, so  in  crossing,  the  greater  or  less  facility  of  one  species 
to  unite  with  another  is  incidental  on  imknown  differences  in 
their  reproductive  systems.  There  is  no  more  reaiion  to  think 
that  species  have  been  specially  endowed  with  various  degrees 


2G4  6UMMAEY.  Chap.  VIH. 

of  sterility  to  prevent  their  crossing  and  blending  in  nature, 
than  to  think  that  trees  have  been  specially  endowed  with  vari- 
ous and  somewhat  analogous  degrees  of  ditliculty  in  being 
grafted  together  in  order  to  prevent  their  inarching  in  our 
forests. 

Tlie  sterility  of  first  crosses  and  of  their  hylirid  progeny  lias 
not,  as  far  as  we  can  judge,  been  acquired  through  natural  se- 
lection. In  the  case  of  first  crosses  it  seems  to  depend  on 
several  circumstances ;  in  some  instances  in  chief  part  on  the 
early  death  of  the  embryo.  In  the  case  of  liybrids,  it  perhajis 
depends  on  tlieir  whole  organization  having  been  disturbed  by 
lieing  compounded  from  two  distinct  forms ;  tlie  sterility  being 
closely  allied  to  that  Avhich  so  frequently  aii'ects  pure  species, 
when  exposed  to  unnatural  conditions  of  life.  This  view  is 
supported  by  a  parallelism  of  another  kind  :  namely,  that,  first, 
the  crossing  of  forms  only  slightly  diiferentiated  favors  the 
vigor  and  fertility  of  their  offspring,  while  close  interbreeding 
is  injurious  ;  and  secondly,  that  slight  changes  in  the  conditions 
of  life  apparently  add  to  the  vigor  and  fertility  of  all  organic 
beings,  while  greater  changes  are  often  injurious.  But  the 
facts  given  on  the  sterility  of  the  illegitimate  unions  of  dimor- 
phic and  trimorphic  plants  and  of  their  illegitimate  progeny, 
render  it  probable  that  some  unknown  bond  in  all  cases  con- 
nects the  degree  of  fertility  of  first  unions  with  that  of  their 
offspring.  The  consideration  of  these  facts  on  dimorphism,  as 
well  as  the  results  of  reciprocal  crosses,  clearly  leads  to  the 
conclusion  that  the  primary  cause  of  tlie  sterility  is  confined  to 
differences  in  the  sexual  elements.  But  why,  in  the  case  of 
species,  the  sexual  elements  should  so  generally  liave  become 
more  or  less  modified,  leading  to  their  mutual  infertility,  we  do 
not  know% 

It  is  not  surprising  that  the  diniculty  in  crossing  any  two 
species,  and  the  sterility  of  their  hybrid-offspring,  should  in 
most  cases  correspond,  even  if  due  to  distinct  causes  ;  for  both 
depend  on  the  amount  of  difference  between  the  species  which 
are  crossed.  Nor  is  it  surprising  that  the  facility  of  effecting 
a  first  cross,  and  the  fertility  of  tlie  hybrids  thus  produced,  and 
the  capacity  of  being  grafted  together — though  this  latter 
capacity  evidently  depends  on  widely-different  circumstances 
— should  all  run,  to  a  certain  extent,  parallel  with  the  system- 
atic afiinity  of  the  forms  subjected  to  experiment ;  for  system- 
atic airiiiity  includes  resemblances  of  all  kinds. 

First  crosses  between  forms  known  to  be  varieties,  or  snffi- 


CuAP.  VIII.  SUMMARY.  205 

cicntly  alike  to  be  considered  as  varieties,  and  their  mongrel 
ofl'spring,  are  very  generally,  but  not,  as  is  so  often  stated, 
invariably  fertile.  Nor  is  this  almost  universal  and  perfect 
fertility  surprising,  Avhen  we  remember  liow  liable  we  are  to 
argue  in  a  circle  with  respect  to  varieties  in  a  state  of  nature ; 
and  when  we  remember  that  the  greater  number  of  varieties 
have  been  jiroduced  under  domestication  by  the  selection  of 
mere  external  difl'crences,  and  that  they  have  not  been  long 
exposed  to  uniform  conditions  of  life.  It  should  also  be  espe- 
cially kept  in  mind,  that  long-continued  domestication  tends  to 
eliminate  sterility,  and  is  therefore  little  likely  to  induce  this 
same  cjuality.  Independently  of  the  question  of  fertility,  in  all 
other  respects  there  is  the  closest  general  resemblance  between 
hybrids  and  mongrels,  in  their  variability,  in  their  power  of 
absorbing  each  other  by  repeated  crosses,  and  in  their  inheri- 
tance of  characters  from  both  parent-forms.  Finally,  then, 
although  we  are  profoundly  ignorant  of  the  precise  cause  of 
the  sterility  of  first  crosses  and  of  h^'brids,  the  facts  given  in 
this  chapter  do  not  seem  to  me  opposed  to  the  belief  that  vari- 
eties and  species  are  not  fundamentally  different. 

12 


2GG  IMPEKFECTIO^'   OF  THE  Chap.  IX. 


CHAPTER   IX. 

ON   TIIK    EMPKRFECTIOX   OF   THE   GEOLOGICAIi   EECOED. 

On  the  Absence  of  Intermediate  Varieties  at  the  Present  Day— On  the  Nature  of  Ex- 
tinct Intermediate  Variotii's :  on  their  Number— On  the  Lapse  of  Time,  as  in- 
ferred from  the  Ilate  of  Denudation  and  of  Deposition — On  the  Lapse  of  Time  as 
estimated  V)y  Years — On  the  Poorness  of  our  Paleontologieal  Collections — on  the 
Denudation  of  Granitic  Areas— On  the  Intermittence  of  Geolo'jrical  Formations — 
On  the  Absence  of  Intermediate  Varieties  in  any  one  Formation— On  the  sudden 
Appearance  of  Groups  of  Species— On  their  sudden  Appearance  in  the  lowest 
known  Fossiliferous  Strata — Antiquity  of  the  Uubitablc  Earth. 

In  the  sixth  chapter  I  enumerated  tlie  chief  objections 
which  iTiio;lit  be  justly  urged  against  the  views  maintained  in 
this  A-olume.  Most  of  them  have  now  been  discussed.  One, 
namely,  the  distinctness  of  specific  forms,  and  their  not  being 
blended  together  by  innumerable  transitional  links,  is  a  very 
obvious  dilliculty.  I  assigned  reasons  why  such  links  do  not 
commonly  occur  at  the  present  day,  under  the  circumstances 
apparently  most  favorable  for  their  presence,  namely,  on  an 
extensive  and  continuous  area  with  graduated  physical  condi- 
tions. I  endeavored  to  show  that  the  life  of  each  species 
depends  in  a  more  important  manner  on  the  presence  of  other 
alrcady-deiined  organic  forms,  than  on  climate  ;  and,  therefore, 
that  the  really  governing  conditions  of  life  do  not  graduate 
away  quite  insensibly  like  heat  or  moisture.  I  endeavored, 
also,  to  show  that  intermediate  varieties,  from  existing  in  lesser 
numbers  than  the  forms  which  they  connect,  will  generally  be 
beaten  out  and  exterminated  during  the  course  of  further 
modification  and  improvement.  The  main  cause,  however,  of 
innumerable  intermediate  links  not  now  occurring  everywhere 
throughout  Nature  depends  on  the  very  process  of  natural 
selection,  through  which  new  varieties  continually  take  the 
places  of  and  exterminate  their  parent-forms.  But  just  in  pro- 
portion as  this  process  of  extermination  has  acted  on  an  enor- 
mous scale,  so  must  tlie  number  of  intermediate  varieties, 
which  have  formerly  existed,  be  truly  enormotis.     ^V^ly,  then, 


CuAP.  IX.  GEOLOGICAL  RECORD.  267 

is  not  every  pfColor;ical  formation  and  every  stratum  full  of 
such  iiitermcdiate  links  V  GeolojTy  assuredly  does  not  reveal 
any  such  tinclv-^radiiated  organic;  chain;  and  this,  perhaps,  is 
the  most  obvious  and  serious  objection  which  can  be  urf^ed 
ar^ainst  the  theor3^  The  explanation  lies,  as  I  believe,  in  the 
extreme  imperfection  of  the  geological  record. 

In  the  first  place,  it  should  always  be  borne  in  mind  what 
sort  of  intermediate  forms  must,  on  the  tiieory,  have  formerly 
existed.  I  have  found  it  diilicult,  when  looking  at  any  two 
species,  to  avoid  picturing  to  myself  forms  directbj  intermedi- 
ate between  them.  But  this  is  a  wholly  false  view  ;  we  should 
alwa3's  look  for  forms  intermediate  between  each  species  and 
a  common  but  unknown  progenitor ;  and  the  progenitor  will 
generally  have  ditlered  in  some  respects  from  all  its  modified 
descendants.  To  give  a  simple  illustration:  the  fantail  and 
pouter  pigeons  have  both  descended  from  the  rock-pigeon; 
if  we  possessed  all  the  intermediate  varieties  which  have  ever 
existed,  we  should  have  an  extremely  close  series  between 
both  and  the  rock-pigeon ;  but  we  should  have  no  varieties 
directly  intermediate  between  the  fantail  and  jiouter ;  none,  for 
instance,  combining  a  tail  somewhat  expanded  with  a  crop 
somewhat  enlarged,  the  characteristic  features  of  these  two 
breeds.  These  two  breeds,  moreover,  have  become  so  much 
modified,  that,  if  we  had  no  historical  or  indirect  evidence  re- 
garding their  origin,  it  would  not  have  been  possible  to  have 
determined,  from  a  mere  comparison  of  their  structure  with 
tliat  of  the  rock-pigeon,  C.  livia,  whether  they  had  descended 
irom  this  species  or  from  some  other  allied  species,  such  as  C. 
oenas. 

So  with  natural  species,  if  we  look  to  forms  very  distinct, 
for  instance  to  the  horse  and  tapir,  we  have  no  reason  to  sup>- 
pose  that  links  ever  existed  directly  intermediate  between 
them,  but  between  each  and  an  unknown  connnon  parent.  The 
common  parent  will  have  had  in  its  whole;  organization  much 
general  resemblance  to  the  tapir  and  to  the  horse  ;  but  in  some 
])oints  of  structure  may  have  difTcMcd  considerably  from  both, 
even  perhaps  more  than  they  differ  from  each  other.  Hence, 
in  all  such  cases,  we  should  be  unable  to  recognize  the  parent- 
form  of  any  two  or  more  s])ecies,  even  if  we  closely  compared 
the  structure  of  the  parent  with  that  of  its  modified  descend- 
ants, unless  at  the  same  time  we  had  a  nearly  jierfect  chain  of 
the  intermediate  links. 

It  is  just  possible  by  the  theory   that  one  of  two  living 


208  THE  LAPSE  OF  TIME.  Chap.  IX, 

forms  might  have  ilescended  from  the  other;  lor  instance,  a 
horse  from  a  tapir ;  and  in  this  case  direct  intermediate  links 
will  have  existed  between  them.  But  such  a  case  "would  im- 
ply that  one  form  had  remained  for  a  very  long  period  unal- 
tered, while  its  descendants  had  undergone  a  vast  amount  of 
change ;  and  the  principle  of  competition  between  organism 
and  organism,  between  child  and  parent,  will  render  this  a  very 
rare  event ;  for  in  all  cases  the  new  and  improved  forms  of  life 
tend  to  supplant  the  old  and  unimproved  forms. 

By  the  theory  of  natural  selection  all  living  species  have 
been  connected  with  the  parent-species  of  each  genus,  by  dif- 
ferences not  greater  than  we  see  between  the  varieties  of  the 
same  species  at  the  present  day ;  and  these  parent-species, 
now  generally  extinct,  have  in  their  turn  been  similarly  con- 
nected with  more  ancient  species ;  and  so  on  backward,  always 
converging  to  the  common  ancestor  of  each  great  class.  So 
that  the  number  of  intermediate  and  transitional  links,  be- 
tween all  living  and  extinct  species,  must  have  been  incon- 
ceivably great.  But  assuredly,  if  this  theory  be  true,  such 
have  lived  upon  the  earth. 

On  the  Lapse  of  Time,  as  inferred  from  the  Mate  of  Deposi- 
tion and  Extent  of  Denudation. 

Ind(^pendently  of  our  not  hnding  fossil  remains  of  such  in- 
finitely numerous  connecting  links,  it  may  be  objected  that 
time  cannot  have  sufficed  for  so  great  an  amount  of  organic 
change,  all  changes  having  been  etlected  very  sIomIv.  It  is 
hardh'  possible  for  me  even  to  recall  to  the  reader,  who  is  not 
a  practical  geologist,  the  facts  leading  the  mind  feebly  to  com- 
prehend the  lapse  of  time.  He  who  can  read  Sir  Cliarles 
Ly ell's  grand  Avork  on  the  Principles  of  Geology,  which  the 
future  historian  will  recognize  as  having  produced  a  revolu- 
tion in  natural  science,  3'et  does  not  admit  how  vast  have  been 
the  past  periods  of  time,  may  at  once  close  this  volume.  Not 
that  it  suffices  to  study  the  Princij^les  of  Geology,  or  to  read 
special  treatises  by  d liferent  observers  on  separate  formations, 
and  to  mark  how  each  author  attempts  to  give  an  inadequate 
idea  of  the  duration  of  each  formation  or  even  of  each  stratum. 
We  can  best  gain  some  idea  of  jiast  time  by  knowing  the  agen- 
cies at  work,  and  learning  how  nuich  of  the  surface  of  the  land 
has  l)cen  denuded,  and  how  nnich  sediment  has  been  deposited. 
As  I.yell  has  well  remarked,  the  extent  and  thickness  of  our 


CiiAP.  IX.  THE  LAl'SK  OF  T1MI<:.  2G9 

sciliincntiiry  formations  arc  the  result  and  the  measure  of  the 
rlrnudation  which  the  eartli's  crust  lias  elsewhere  under<roue. 
Therefore  a  man  should  examine  for  himself  the  great  piles  of 
superimposed  strata,  and  watch  the  rivulets  brini^ini^  down 
niuil,  and  the  waves  wearing  away  the  sca-clills,  in  order  to 
comprehend  something  about  the  duration  of  past  time,  the 
monuments  of  which  we  sec  all  around  us. 

It  is  good  to  wander  along  the  coast,  when  formed  of  raod- 
eratcly-hard  rocks,  and  mark  the  process  of  degradation.  The 
tides  in  most  cases  reach  the  cliffs  only  for  a  short  time  twice  a 
day,  and  the  waves  cat  into  them,  only  when  they  are  charged 
with  sand  or  pel)bles ;  for  there  is  good  evidence  that  pure 
water  elfects  nothing  in  wearing  away  rock.  At  last  the  base 
of  the  cliff  is  undermined,  huge  fragments  fall  down,  and  these, 
remaining  fixed,  have  to  be  worn  away  atom  by  atom,  until 
after  being  reduced  iii  size  they  can  be  rolled  about  by  the 
waves,  and  then  they  are  more  quickly  ground  into  pebbles, 
sand,  or  mud.  But  how  often  do  we  see  along  the  bases  of 
retreating  cliffs  rounded  bowlders,  all  thickly  clothed  by  marine; 
productions,  showing  how  little  they  are  abraded,  and  how 
seldom  they  are  rolled  about !  Moreover,  if  we  follow  for  a 
few  miles  any  line  (jf  rocky  cliff,  which  is  undergoing  degrada- 
tion, we  find  that  it  is  only  here  and  there,  along  a  sliort  length 
or  round  a  promontory,  that  the  clifl's  arc  at  the  present  time 
suffering.  The  appearance  of  the  surface  and  the  vegetation, 
show  that  elsewhere  yeai'S  have  elapsed  since  the  Avaters 
washed  their  base. 

We  have,  however,  recently  learned  from  the  observations 
of  Ramsay,  in  the  van  of"  excellent  observers,  of  Jukes,  Geikie, 
Croll,  and  others,  that  subaerial  degradation  is  a  much  more 
imi)ortant  agency  than  coast-action,  or  the  power  of  the  waves. 
Tiie  whole  surface  of  the  land  is  exposed  to  the  chemical  ac- 
tion of  the  air  and  of  the  rain-water  with  its  dissolved  carbonic 
acid,  and  in  colder  countries  to  frost;  the  disintegrated  matter 
is  carried  down  even  gentle  slopes  during  heavy  rain,  and  to  a 
greater  extent  than  might  be  supposed,  especially  in  arid  dis- 
tricts, by  the  wind  ;  it  is  then  transported  by  the  streams  and 
rivers,  which  when  rapid  deepen  their  chainicls,  and  triturate 
the  fragments.  On  a  rainy  day,  even  in  a  gently-undulating 
country,  we  see  the  effects  of  subaerial  degradation  in  the  mud- 
dy rills  Avhich  flow  down  each  slope.  Messrs.  Kamsay  and 
Whitaker  have  shown,  and  the  observation  is  a  most  striking 
one,  that  the  great  lines  of  escarpment  in  the  Wcaldon  district 


270  '^^iE  LAPSE  OF  TIME.  CiiAr.  IX. 

and  those  ranging  across  England,  which  formerly  were  looked 
at  by  every  one  Jis  ancient  sea-coasts,  cannot  have  been  thus 
formed,  for  each  line  is  composed  of  one  and  the  s;une  forma- 
tion, while  our  j^resent  sea-clifls  are  eveiywhere  formed  by  the 
intersection  of  various  formations.  This  being  tlic  case,  we 
are  compcllcil  to  admit  that  the  escaq^ments  owe  their  origin 
in  chief  part  to  the  rocks  of  Avhich  they  are  composed  having 
resisted  subacrial  denudation  better  than  the  surrounding  sur- 
face ;  this  surface  consequently  has  l^een  gradually  lowered, 
with  the  lines  of  harder  rock  left  projecting.  Nothing  im- 
presses the  mind  with  the  vast  duration  of  time,  according  to 
our  ideas  of  time,  more  forcibly  tlian  the  conviction  thus  gained 
that  subaiirial  agencies,  which  apparently  have  so  little  power, 
and  which  seem  to  work  so  slowly,  have  produced  such  great 
results. 

When  thus  impressed  with  the  slow  rate  at  Vv'liich  tlie  land 
is  worn  away  through  subaerial  and  littoral  action,  it  is  good, 
in  order  to  appreciate  the  past  duration  of  time,  to  consider,  on 
the  one  hand,  the  mass  of  rock  which  has  been  removed  over 
many  extensive  areas,  and  on  the  other  hand  the  tliickness  of 
our  sedimentary  formations.  I  remember  haAnng  been  much 
struck  M'hen  viewing  volcanic  islands,  which  have  been  worn 
by  the  waves  and  pared  all  around  into  perpendicular  cliffs  of 
one  or  two  thousand  feet  in  height ;  for  the  gentle  slope  of 
the  lava-streams,  due  to  their  formerly  liquid  state,  showed  at 
a  glance  how  far  the  hard,  rocky  beds  had  once  extended  into 
the  open  ocean.  The  same  story  is  told  still  more  plainly  by 
faults — those  great  cracks  along  which  the  strata  have  been 
upheaved  on  one  side,  or  thrown  down  on  the  other,  to  the 
height  or  depth  of  thousands  of  feet ;  for  since  the  crust  cracked, 
and  it  makes  no  great  difference  whether  the  upheaval  was 
sudden,  or,  as  most  geologists  now  believe,  was  very  slow  and 
eflected  by  many  starts,  the  surface  of  the  land  has  been  so 
completely  planed  down  that  no  trace  of  these  vast  dislocations 
is  externally  visible.  The  Craven  fault,  for  instance,  extends 
for  upward  of  thirty  miles,  and  along  this  line  the  vertical  dis- 
placement of  tlie  strata  varies  from  600  to  3,000  feet.  Prof, 
liamsay  has  published  an  account  of  a  downtlirow  in  Anglesea 
of  2,300  feet;  and  lie  informs  me  tliat  he  fully  believes  that 
tliere  is  one  in  ]M(>rionethshire  of  12,000  feet;  yet  in  these 
cas(>s  there  is  nothing  on  the  sm-face  of  the  land  to  show  such 
prodigious  movements ;  tlie  jiile  of  rocks  on  cither  side  of  the 
crack  having  been  smoothly  SAvej)t  away. 


Chap.  IX.  THE  LAPSE  OF  TIME.  271 

Oil  the  other  Imnd,  in  all  parts  of  the  world  the  piles  of 
Kcdimentary  strata  arc  of  wonderful  thickness.  In  the  Cordil- 
lera I  estimated  one  mass  of  cono:lomcrate  at  ten  thousand 
feet ;  and  althou_Q;h  conf2;lomerates  have  probably  been  accu- 
nuilated  at  a  quicker  rate  than  liner  sediments,  yet  from  being 
formed  of  worn  and  rounded  pebbles,  each  of  which  bears  the 
stamp  of  time,  they  are  f:^ood  to  show  how  slowly  tlic  mass 
must  have  been  heaped  to<j;'ether.  Prof.  Ramsay  has  <;iven  me 
the  niaxiir.um  thickness,  from  actual  measurement  in  most 
cases,  of  the  successive  formations  in  dijf'ercnt  parts  of  Great 
Britain;  and  this  is  the  result: 

Feet. 

Paleozoic  BtratA  (not  including?  igneous  beds) 57,154 

Secondary  strata 13.100 

Tertiary  strata 2,240 

— makinfi;'  altogether  72,584  feet ;  that  is,  very  nearly  thirteen 
and  three-(iuarters  British  miles.  Some  of  the  formations, 
Avhich  are  represented  in  England  by  thin  beds,  are  thousands 
of  feet  in  thickness  on  the  Continent.  Moreover,  between  each 
successive  formation,  we  have,  in  the  o])inion  of  most  geolo- 
gists, enormously  long  blank  periods.  So  that  the  lofty  pile 
of  sedimentary  rocks  in  Britain  gives  but  an  inadequate  idea 
of  the  time  which  has  elapsed  during  their  accumulation.  The 
consideration  of  these  various  facts  impresses  the  mind  almost 
in  the  same  manner  as  does  the  vain  endeavor  to  grapple  with 
the  idea  of  eteniity. 

Nevertheless  this  impression  is  partly  false.  Mr.  Croll,  in 
a  most  interesting  paper,  remarks  that  we  do  not  err  "  in  form- 
ing too  great  a  conception  of  the  length  of  geological  periods," 
but  in  estimating  them  by  years.  When  geologists  look  at 
large  and  complicated  phenomena,  and  then  at  the  figures  rep- 
resenting several  million  years,  the  two  produce  a  totally  dif- 
ferent effect  on  the  mind,  and  the  figures  are  at  once  pro- 
nounced to  be  too  small.  But  in  regard  to  denudation,  Mr. 
Croll  shows,  by  calculating  the  known  amount  of  sediment  an- 
nually brought  down  by  certain  rivers,  relatively  to  the  areas 
of  drainage,  that  1,000  feet  of  rock,  disintegrated  through  sub- 
ai'rial  agenci(>s,  would  thus  be  removed  from  the  mean  level  of 
the  whoh*  area  in  the  course  of  six  million  vears.  This  seems 
an  astonishing  result,  and  some  considerations  lead  to  the  sus- 
picion that  it  may  be  much  too  large,  but  even  if  halved  or 
(juartered  it  is  still  very  surprising.  Few  of  us,  however,  know 
what  a  million    really  means:  Mr.  Croll  gives  the  following 


272  Tilt:   LAPSE  OF  TIME.  Cuap.  IX. 

illustration :  take  a  narrow  strip  of  paper,  83  feet  4  inclies  in 
length,  and  stretch  it  along  the  Avail  of  a  large  hall ;  then  mark 
off  at  one  end  the  tenth  of  an  inch.  This  tenth  of  an  inch  will 
represent  one  hundred  years,  and  the  entire  strip  a  million  years, 
But  let  it  be  borne  in  mind,  in  relation  to  the  subject  of 
this  work,  what  a  hundred  years  implies,  represented  as  it  is 
by  a  measure  utterly  insignificant  in  a  hall  of  the  above  dimen- 
sions. Several  eminent  breeders,  during  a  single  lifetime,  have 
so  largely  modified  some  of  the  higher  animals,  Avhich  propa- 
gate their  kind  much  more  slowly  than  most  of  the  lower  ani- 
mals, that  they  have  formed  Avliat  Avell  deserve  to  be  called 
new  sub-breeds.  Few  men  have  attended  AA-ith  due  care  to 
any  one  strain  for  more  than  half  a  century,  so  that  a  hundred 
years  represent  the  Avork  of  two  breeders  in  succession.  It  is 
not  to  be  supposed  that  species  in  a  state  of  nature  ever 
change  so  quickly  as  domestic  animals  under  the  guidance  of 
methodical  selection.  The  comparison  Avould  be  in  every  AA'ay 
fairer  Avitli  the  results  Avhich  follow  from  unconscious  selection, 
that  is,  the  preservation  of  the  most  useful  or  beautiful  animals, 
Avith  no  intention  of  modifying  the  breed  ;  but  by  this  process 
of  unconscious  selection,  various  breeds  haA"e  been  sensibly 
changed  in  the  course  of  two  or  three  centuries. 

Species,  however,  probably  change  much  more  slowly,  and 
within  the  same  country  only  a  few  change  at  the  same  time. 
This  slowness  follows  from  all  the  inhabitants  of  the  same 
country  being  already  so  avcU  adapted  to  each  other  that  ncAV 
places  in  the  polity  of  Nature  do  not  occiir  until  after  long  in- 
tervals, Avhen  changes  of  some  kind  in  the  physical  conditions 
or  through  immigration  haA^e  occurred;  and  indiA^idual  differ- 
ences or  variations  of  the  right  nature,  by  Avliich  some  of  the 
inhabitants  might  be  better  fitted  to  their  new  places  under 
the  altered  circumstances,  might  not  at  once  occur.  According 
to  the  standard  of  years  Ave  have  no  means  of  determining 
how  long  a  period  it  takes  to  modify  a  species.  Mr.  Croll, 
judging  from  the  amount  of  heat-energy  in  the  sun  and  from 
the  date  Avhich  he  assigns  to  the  last  glacial  epoch,  estimates 
that  only  sixty  million  years  lia\'e  elapsed  since  the  deposi- 
tion of  the  first  Cambrian  formation.  This  appears  a  A'ery 
short  period  for  so  many  and  such  great  mutations  in  the  forms 
of  life  as  have  certainly  since  occurred.  It  is  admitted  that 
many  of  the  elements  in  the  calculation  are  more  or  less  doubt- 
ful, and  Sir  "W.  Thomson  giA'Cs  a  Avide  margin  to  the  possible 
age  of  the  habitable  Avorld.     But,  as  Ave  have  seen,  Ave  cannot 


Chap.  IX.  PALEONTOLOGICAL  COLLECTIONS.  273 

comprehend  what  tlio  firrures  00,000,000  really  imply ;  and 
during  this,  or  perhaps  a  lonfrcr  roll  of  years,  the  land  and  the 
waters  have  everywhere  teemed  with  livinj^  creatures,  all  ex- 
posed to  the  struggle  for  life  and  undergoing  change. 

On  the  Poorness  of  oitr  Paleontological  Collections. 

Now  let  us  turn  to  our  richest  geological  museums,  and 
what  a  paltry  display  we  behold  !  That  our  collections  arc 
very  imperfect  is  admitted  by  every  one.  The  remark  of  that 
admira1:)lc  paleontologist,  Edward  Forbes,  should  not  be  for- 
gotten, namely,  that  numbers  of  our  fossil  species  are  known 
and  named  from  single  and  often  broken  specimens,  or  from  a 
few  specimens  collected  on  some  one  spot.  Only  a  small  portion 
of  the  surface  of  the  earth  has  been  geologically  explored,  and 
no  part  with  sufficient  care,  as  the  important  discoveries  made 
eVery  year  in  Europe  prove.  No  organism  wholly  soft  can  be 
preserved.  Shells  and  bones  Avill  decay  and  disappear  when 
left  on  the  bottom  of  the  sea,  where  sediment  is  not  accumu- 
lating. I  believe  we  often  take  an  erroneous  view,  when  we 
tacitly  admit  to  ourselves  that  sediment  is  being  deposited 
over  nearly  the  whole  bed  of  the  sea,  at  a  rate  sufficiently 
quick  to  embed  and  preserve  fossil  remains.  Throughout  an 
enormously  large  proportion  of  the  ocean,  the  bright  blue  tint 
of  the  water  bespeaks  its  purity.  The  many  cases  on  record 
of  a  formation  conformably  covered,  after  an  immense  interval 
of  time,  by  another  and  later  formation,  Avithout  tlic  underly- 
ing bed  having  suffered  in  the  interval  any  wear  and  tear,  seem 
explicable  only  on  the  view  of  the  l)ottom  of  the  sea  not  rarely 
lying  for  ages  in  an  unaltered  condition.  The  remains  Avhich 
do  become  embedded,  if  in  sand  or  gravel,  will  when  the  beds 
are  upraised  generally  be  dissolved  by  the  percolation  of  rain- 
water chargetl  with  carbonic  acid.  Some  of  the  many  kinds 
of  animals  which  live  on  the  beach  between  high  and  low 
water  mark  seem  to  be  rarely  jireserved.  For  instance,  the 
several  species  of  the  Chthamalin;!:?  (a  sub-family  of  sessile 
cirripcdes)  coat  the  rocks  all  over  the  world  in  infinite 
numbers:  they  are  all  slridly  littoral,  with  the  exception  of  a 
single  Medit(;rranean  species,  which  inhabits  deep  water,  and 
this  has  been  f(jund  fossil  in  Sicily,  whereas  not  one  other 
species  has  hitherto  been  found  in  any  tertiary  formation  :  yet 
it  is  not  known  that  the  genus  Chthamalus  existeil  during  the 
T^halk  period.     Lastly,  many  great  deposits  requiring  a  vast 


274  THE  .POORNESS  OF  OUR  Chap.  IX, 

length  of  time  for  llicir  Jiccuinuliilion,  are  entirely  destitute  of 
organic  remains,  witliout  our  being  able  to  assign  any  reason  : 
one  of  tlic  most  striking  instances  is  that  of  the  Flysch  forma- 
tion, -wliich  consists  of  shale  and  sandstone,  several  thousand, 
occasionally  even  six  thousand  feet,  in  thickness,  and  extending 
for  at  least  300  miles  from  Vienna  to  Switzerland ;  and,  al- 
though this  great  mass  has  been  most  carefully  searched,  no 
fossils,  except  a  fcAv  vegetable  remains,  have  been  found. 

"With  respect  to  the  terrestrial  productions  which  lived 
during  the  Secondary  and  Paleozoic  periods,  it  is  superfluous 
to  state  that  our  evidence  from  fossil-remahis  is  fragmentary 
in  an  extreme  degree.  For  instance,  not  a  land-shell  until  quite 
recently  was  known  belonging  to  cither  of  these  vast  periods, 
with  the  exception  of  one  species  discovered  by  Sir  C.  Lyell 
and  Dr.  DaAvsou  in  the  carboniferous  strata  of  North  Amei'ica, 
of  which  shell  above  a  hundred  specimens  have  now  been  col- 
lected. In  regard  to  mammiferous  remains,  a  single  glance  at  the 
historical  table  published  inLyell's  Manual  will  bring  home  the 
Iruth,  how  acciilental  and  rare  is  tlicir  preservation,  far  better 
than  pages  of  detail.  Nor  is  their  rarity  surprising,  when  we 
remember  how  large  a  proportion  of  the  bones  of  tertiary  mam- 
mals have  been  discovered  either  in  caves  or  in  lacustrine 
deposits;  and  that  not  a  cave  or  true  lacustrine  bed  is  known 
belonging  to  the  age  of  oiu-  secondary  or  paleozoic  formations. 

But  the  imperfection  in  the  geological  record  largely  results 
from  another  and  more  important  cause  than  any  of  the  forego- 
ing ;  namely,  from  the  several  formations  being  separated  from 
each  other  l^y  wide  intervals  of  time.  This  doctrine  has  been 
most  emphatically  admitted  by  many  geologists  and  paleon- 
tologists, who,  like  E.  Forbes,  entirely  disbelieve  in  the  change 
of  species.  When  we  see  tiie  formations  tabulated  in  written 
works,  or  when  we  follow  them  in  Nature,  it  is  diihcult  to 
avoid  believing  that  they  arc  closely  consecutive.  But  we 
know,  for  instance,  from  Sir  R.  Murchison's  great  work  on  Rus- 
sia, what  wide  gaps  there  are  in  that  country  between  the 
superimposed  formations ;  Sf)  it  is  in  North  America,  and  in 
many  otlier  parts  of  the  world.  The  most  skilful  geologist,  if 
his  attention  had  been  confined  exclusively  to  tliese  large  ter- 
ritories, Avould  never  have  suspected  that,  during  the  periods 
which  were  blank  and  barren  in  his  own  country,  great  piles 
of  sediment,  charged  Avith  new  and  peculiar  forms  of  life,  had 
elsewhere  been  accumulated.  And  if,  in  each  separate  territory, 
hardly  any  idea  can  be  formed  of  the  length  of  time  which  has- 


CiiAP.  IX.  PALEONTOLOGICAL  COLLECTIONS.  075 

elapsed  lictwoL'u  Iho  consecutive  formations,  we  may  infer  that 
this  could  nowhere  be  ascertained.  The  frequent  and  great 
changes  in  the  miiieralogieal  composition  of  consecutive  forma- 
tions, generall}^  implying  great  changes  in  the  geography  of 
the  surronnding  lands,  whence  the  sediment  has  been  derived, 
accords  with  tlie  belief  of  vast  intervals  of  time  having  elapsed 
between  each  formation. 

But  we  can,  I  thinlc,  see  wliy  the  geological  formations  of 
each  region  are  almost  invariably  intermittent;  that  is,  have 
not  followed  each  other  in  close  sequence.  Scarcely  any  fact 
struck  me  more  when  examining  many  hundred  miles  of  the 
South  American  coasts,  which  have  been  uj)raised  several  hun- 
dred feet  Avithin  the  recent  period,  than  the  absence  of  any 
recent  deposits  sufliciently  extensive  to  last  for  even  a  short 
geological  period.  Along  the  whole  west  coast,  Avhich  is  in- 
liabited  by  a  peculiar  marine  fauna,  tertiary  beds  are  so  poorly 
cTeveloped,  that  no  'record  of  several  successive  and  peculiar 
marine  faunas  will  probably  be  preserved  to  a  distant  age.  A 
little  refl(^ction  will  explain  Avhy,  along  the  rising  coast  of  the 
western  side  of  South  America,  no  extensive  formations  with 
recent  or  tertiary  remains  can  anywhere  be  found,  though  the 
supply  of  sediment  must  for  ages  have  been  great,  from  the 
enormous  degradation  of  the  coast-rocks  and  from  muddy 
streams  entering  the  sea.  The  exjilanation,  no  doubt,  is,  that 
the  littoral  and  sub-littoral  deposits  are  continually  worn  away 
as  soon  as  they  nro,  lirought  up  by  the  slow  and  gradual  rising 
of  the  land  witliin  the  grinding  action  of  the  coast-waves. 

We  niay,  I  think,  conclude  that  sediment  must  be  accumu- 
lated in  extremely  thick,  solid,  or  extensive  masses,  in  order 
to  withstand  the  incessant  action  of  tlie  waves,  wlien  lirst  up- 
raised and  during  successive  oscillations  of  level,  as  well  as 
the  subsequent  subaerial  degradation.  Such  thick  and  exten- 
sive accumulations  of  sediment  may  be  formed  in  two  waj-s; 
either  in  profound  depths  of  the  sea,  in  which  case  the  bottom 
will  not  be  inhabited  by  so  many  and  such  varied  f(jrms  of  life 
as  the  more  shallow  seas;  and  the*  mass  Avhen  upraised  will 
give  an  imperfect  record  of  the  organisms  which  existed 
tliroughout  the  world  during  the  period  of  its  accunuilation; 
or,  sediment  may  be  deposited  to  any  thickness  and  extent 
over  a  shallow  bottom,  if  it  continue  slowly  to  subside.  In 
this  latter  case,  as  hmg  as  the  rate  of  subsidence  and  the  suj> 
ply  of  sediment  nearly  balance  each  other,  the  sea  will  remain 
shallow  and  favorable  for  many  and  varied  fonns,  and  thus  a 


276  THE  POORNESS  OF  OUR  Chap.  IX. 

rich  fossiliferous  formation,  thick  cnougli,  \\hvn  upraised,  to 
resist  a  large  amount  of  denudation,  may  be  formed. 

I  am  convinced  that  nearly  all  our  ancient  formations,  which 
are  throughout  the  greater  part  of  their  thickness  rlcJi  in  fos- 
sils, have  thus  been  formed  during  subsidence.  Since  publish- 
ing my  views  on  this  subject  in  1845, 1  have  watched  the  prog- 
ress of  Geology,  and  have  been  surprised  to  note  how  author 
after  author,  in  treating  of  this  or  that  great  formation,  has 
come  to  the  conclusion  that  it  was  accumulated  during. sub- 
sidence. I  may  add  that  the  only  ancient  tertiary  formation 
on  the  west  coast  of  South  America,  which  has  been  bulky 
enough  to  resist  such  degradation  as  it  has  as  yet  suffered,  but 
which  will  hardly  last  to  a  distant  geological  age,  was  deposit- 
ed during  a  downward  oscillation  of  level,  and  thus  gained 
considerable  thickness. 

All  geological  facts  toll  us  plainly  that  each  area  has  under- 
gone numerous  slow  oscillations  of  level,  atid  apparently  these 
oscillations  have  affected  Avide  spaces.  Consequently  forma- 
tions rich  in  fossils  and  sufficiently  thick  and  extensive  to  re- 
sist subsequent  degradation,  may  have  been  formed  over  wide 
spaces  during  periods  of  subsidence,  but  only  where  the  sup- 
ply of  sechment  was  sufficient  to  keep  the  sea  shallow  and  to 
embed  and  preserve  the  remains  before  they  had  time  to  deca3% 
On  the  other  hand,  as  long  as  the  bed  of  the  sea  remained  sta- 
tionary, thich  deposits  could  not  hare  been  accumulated  in  the 
shallow  parts,  which  are  the  most  favorable  to  life.  Still  less 
could  this  have  happened  during  the  alternate  periods  of  ele- 
vation ;  or,  to  speak  more  accurately,  the  beds  which  were 
then  accumulated  Avill  generally  have  been  destroyed  by  being 
upraised  and  brought  within  the  limits  of  the  coast-action. 

These  remarks  appl}'"  chiefly  to  littoral  and  sub-littoral  de- 
jiosits.  In  the  case  of  an  extensive  and  shallow  sea,  such  as 
that  within  a  large  part  of  the  Malay  Archipelago,  Avhere  the 
depth  varies  from  30  or  40  to  60  fathoms,  widely-extended  for- 
mation might  be  formed  during  a  jicriod  of  elevation,  and  yet 
not  suffer  excessively  fr©m  denudation  during  its  slow  up- 
heaval ;  but  the  thickness  of  the  formation  could  not  be  great, 
for  owing  to  the  elevatory  movement  it  would  be  less  than  the 
depth  in  whidi  it  was  formed  ;  nor  would  the  deposits  be  much 
consolidated,  nor  be  cajiped  by  ovcrlj-ing  formations,  so  that 
it  would  run  a  good  chance  of  being  worn  away  by  atmos- 
])heric  dc^gradation  and  by  the  action  of  the  sea  during  subse- 
quent oscillations  of  level.     It  has,  however,  been  suggested 


CiiAr.  IX.  TALEONTOLOGICAL  COLLECTIONS.  277 

by  Mr.  Hopkins,  lliat  if  one  part  of  the  area,  after  rising  and 
before  being  denuded,  subsided,  the  deposit  formed  during  the 
rising  movement,  though  not  thick,  might  afterward  become 
protected  by  fresh  accumuhitions,  and  thus  be  jireserved  for  a 
long  period. 

Mr.  Hopkins  also  expresses  his  belief  that  sedimentary  beds 
of  considerable  horizontal  extent  have  rarely  been  completely 
destroyed.  But  all  geologists,  excepting  the;  few  who  believe 
that  our  present  metamorphic  schists  and  plutonic  rocks  once 
formed  the  primordial  nucleus  of  the  globe,  Avill  admit  that 
tlicse  latter  rocks  have  been  denuded  on  an  enormous  scale. 
For  it  is  scarcely  possible  that  such  rocks  could  have  been 
solidilied  and  crystallized  while  imcovered ;  but  if  the  meta- 
morphic action  occurred  at  profound  depths  of  the  ocean,  the 
former  protecting  mantle  of  rock  may  not  have  been  very  thick. 
Admitting,  then,  that  gneiss,  mica-schist,  granite,  diorite,  etc., 
w-ere  once  necessarily  covered  up,  how  can  we  account  for  the 
naked  and  extensive  areas  of  such  rocks  in  many  jiarts  of  the 
world,  except  on  the  belief  that  they  have  subsequently  been 
completely  denuded  of  all  overl^ang  strata  ?  lliat  such  ex- 
tensive areas  do  exist  cannot  be  doubted  :  the  granitic  region 
of  Parime  is  described  by  Humboldt  as  being  at  least  nineteen 
times  as  large  as  Switzerland.  South  of  the  Amazon,  Boue 
colors  an  area  comjiosed  of  rocks  of  this  nature  as  equal  to  tliat 
of  Spain,  France,  Italy,  part  of  German}-,  and  the  British  Isl- 
ands, all  conjoined.  This  region  has  not  been  carefully  ex- 
plored, but,  from  tlie  concurrent  testimony  of  travellers,  the 
granitic  area  is  very  large :  thus.  Von  Eschwege  gives  a  de- 
tailed section  of  these  rocks,  stretching  from  Rio  dc  Janeiro 
for  260  geograjihical  miles  inland  in  a  straight  line ;  and  I  trav- 
elled for  150  miles  in  another  direction,  and  saw  nothing  but 
granitic  rocks.  Numerous  specimens,  collected  along  the  whole 
c(jast  from  near  Rio  Janeiro  to  tlie  mouth  of  the  Plata,  a  dis- 
tance of  1,100  geographical  miles,  were  examined  l)y  me,  and 
they  all  belonged  to  this  class.  Inland,  along  the  whole  north- 
ern bank  of  the  Plata,  I  saw,  besides  modern  tertiary  beds,  only 
one  small  patch  of  slightly-metamorphosed  rock,  ^\■hich  alone 
could  have  formed  a  part  of  the  original  capping  of  the  granitic 
scries.  Tuining  to  a  well-known  region,  namely,  to  the  United 
States  and  Canada,  as  shown  in  Prof.  II.  I).  Rogers's  beauti- 
ful map,  I  have  estimated  the  areas  l)y  (Hitting  out  and  weigh- 
ing the  paper,  and  I  find  that  liie  metamorphic  (including  "the 
Henii-metamorphic")  and  granitic  rocks  exceed,  in  the  i)n)p()rtion 


273  ABSENCE   OF  INTERMEDIATE   VARIETIES      Chap.  IX. 

of  19  to  1:2.5,  the  Avholc  of  the  newer  Paleozoic  formations. 
In  many  rcg'ions  the  metamorphic  and  granitic  rocks  would  be 
seen  to  be  much  more  widely  extended,  if  all  the  sedimentary 
beds  Averc  removed  which  rest  unconformably  on  them,  and 
whicli  could  not  have  formed  part  of  the  original  mantle  under 
which  they  were  crystallized.  Hence  it  is  probable  that  in  some 
parts  of  the  world  whole  formations  have  been  completely  de- 
nuded, with  not  a  wreck  left  behind. 

One  remark  is  here  worth  a  passing  notice.  During  peri- 
ods of  elevation  the  area  of  the  land  and  of  the  adjoining  shoal 
parts  of  the  sea  will  be  increased,  and  new  stations  will  often 
be  formed — all  circumstances  favorable,  as  previously  explained, 
for  the  formation  of  new  varieties  and  species  ;  but  during  such 
periods  there  will  generally  be  a  blank  in  the  geological  record. 
On  the  other  hand,  during  subsidence,  the  inhabited  area  and 
number  of  inhabitants  Avill  decrease  (excepting  on  the  shores 
of  a  continent  when  fii-st  broken  up  into  an  archipelago),  and 
consequently  during  subsidence,  though  there  will  bo  much  ex- 
tinction, few  new  varieties  or  species  will  be  formed ;  and  it 
is  during  these  very  periods  of  subsidence  that  the  deposits 
which  are  richest  in  fossUs  have  been  accumulated. 

On  the  Absence  of  JVumcrous  Intermediate  Varieties  in  any 
one  Single  Formatio7i, 

From  these  several  considerations,  it  cannot  be  doubted 
that  the  geological  record,  viewed  as  a  whole,  is  extremely  im- 
perfect ;  but  if  we  conline  our  attention  to  any  one  formation, 
it  becomes  much  more  diilicult  to  understand  why  we  do  not 
therein  find  closely-graduated  varieties  between  the  allied 
species  which  lived  at  its  commencement  and  at  its  close. 
Several  cases  arc  on  record  of  the  same  species  presenting  va- 
rieties in  the  upper  and  lower  parts  of  the  same  formation : 
thus,  Trautschold  gives  a  number  of  instances  with  Ammon- 
ites ;  and  Hilgendorf  has  described  a  most  curious  case  of  ten 
graduated  forms  of  Planorbis  multiformis  in  the  successive 
beds  of  a  fresh-water  formation  in  Switzerland.  Although 
each  formation  has  indisputably  required  a  vast  number  of 
years  for  its  deposition,  several  reasons  can  be  given  why  each 
should  not  connnonly  include  a  graduated  series  of  links  be- 
tween the  species  which  lived  at  its  commencement  and  close; 
but  I  cannot  assign  due  proportional  weight  to  the  following 
considerations. 


CiiAr.  IX.  IN  ANY  SINGLE  lORMATION.  219 

Although  each  formation  may  mark  a  very  long  lapse  of 
years,  each  probably  is  short  compared  with  the  period  requi- 
site to  change  one  sjieoies  into  another.  I  am  aware  that  two 
paleontologists,  whose  opinions  are  worthy  of  much  deference, 
namely,  Broim  and  AVoodward,  have  concluded  that  the  aver- 
age duration  of  each  fcjrmation  is  twice  or  thrice  as  long  as  the 
average  duration  of  specific  forms.  But  insuperable  difficul- 
ties, as  it  seems  to  me,  prevent  us  from  coming  to  an}"^  just 
conclusion  on  this  head.  W^hen  we  see  a  species  first  appear- 
ing in  the  middle  of  any  formation,  it  would  be  rash  in  the  ex- 
treme to  infer  that  it  had  not  elsewhere  previously  existed. 
So,  again,  when  we  find  a  species  disappearing  before  the  last 
layers  have  been  deposited,  it  would  be  equally  rash  to  sup- 
pose that  it  then  became  extinct.  We  forget  how  small  the 
area  of  Europe  is  compared  with  the  rest  of  the  world ;  nor 
have  the  several  stages  of  the  same  formation  throughout  Eu- 
rope been  correlated  Avith  perfect  accuracy. 

With  marine  animals  of  all  kinds,  we  may  safelv  infer  a 
large  amount  of  migration  during  climatal  and  other  changes  ; 
and  when  we  see  a  species  first  appearing  in  any  formation,  the 
probability  is,  that  it  only  then  first  iimnigrated  into  that  area. 
It  is  well  known,  for  instance,  that  several  species  ajipeared 
somewhat  earlier  in  the  paleozoic  beds  of  North  America  than 
in  those  of  Europe;  time  having  apparently  been  required  for 
their  Tnigration  from  the  American  to  the  European  seas.  In 
examining  the  latest  deposits  in  various  quai'ters  of  the  world, 
it  has  everywhere  been  noted  that  some  few  still  existing  spe- 
cies are  common  in  the  deposit,  but  have  become  extinct  in  the 
immediately  surrounding  sea ;  or,  conversely,  that  some  arc 
now  abundant  in  the  neighboring  sea,  but  are  rare  or  absent  in 
tliis  particular  deposit.  It  is  an  excellent  lesson  to  reflect  on 
the  ascertained  amount  of  migration  of  the  inhabitants  of  Eu- 
rope during  the  glacial  epoch,  which  forms  only  a  part  of  one 
whole  geolf)gical  period  ;  and  likewise  to  reflect  on  the  changes 
of  level,  on  the  extreme  change  of  climate,  and  on  the  great 
lapse  of  time — all  included  within  this  same  glacial  period.  Yet 
it  may  be  doubted  whether,  in  any  quarter  of  the  world,  sedi- 
mentary deposits,  indiidlitf/  fossil  rcmahis,  have  gone  on  ac- 
cumulating within  the  same  area  during  the  whole  of  this 
period.  It  is  not,  for  instance,  probable  that  S(Mliment  was  de- 
posited during  the  whole  of  the  glacial  jieriod  near  the  mouth 
of  the  Mississippi,  within  that  limit  of  (ie])th  at  which  marine 
animals  can  best  flourish  ;  for  we  know  that  great  geographical 


280  ABSENCE  OF  INTERMEDIATE  VARIETIES      Chap.  IX. 

changes  oocurrcd  in  other  parts  of  America  duriiifr  this  space 
of  time.  "\\'h(ui  such  beds  as  were  deposited  in  shallow  water 
near  the  mouth  of  the  Mississippi  during  some  part  of  the  gla- 
cial period  shall  have  been  upraised,  organic  remains  will  prob- 
ably lirst  appear  and  disappear  at  different  levels,  owing  to 
the  migrations  of  species  and  to  geographical  changes.  And 
in  the  distant  future,  a  geologist,  examining  these  beds,  would 
be  tempted  to  conclude  that  the  average  duration  of  life  of  the 
embedded  fossils  had  been  less  than  that  of  the  glacial  period, 
instead  of  having  been  really  far  greater,  that  is,  extending 
from  before  the  glacial  ejioch  to  the  present  day. 

In  order  to  get  a  perfect  gradation  between  two  forms  in 
the  upper  and  lower  parts  of  the  same  formation,  the  deposit 
will  have  to  go  on  continuously  accumulating  during  a  very 
long  period,  so  that  there  may  be  time  sufficient  for  the  slow 
procT^ss  of  modification ;  hence  the  deposit  will  have  to  be  a 
very  thick  one ;  and  the  species  undergoing  change  will  have 
to  live  in  the  same  district  throughout  this  whole  time.  But 
we  have  seen  that  a  thick  formation,  fossiliferous  throughout 
its  entire  thickness,  can  accumulate  only  during  a  period  of 
subsidence ;  and  to  keep  the  depth  approximately  the  same, 
which  is  necessary  that  the  same  marine  species  may  hve  on 
the  same  space,  the  supply  of  sediment  must  nearly  counter- 
balance the  amount  of  subsidence.  But  this  same  movement 
of  subsidence  will  tend  to  submerge  the  area  whence  the  sedi- 
ment is  derived,  and  thus  diminish  the  supply  while  the  down- 
ward movement  continues.  In  fact,  this  nearly  exact  balancing 
between  the  supply  of  sediment  and  the  amount  of  subsidence 
is  probably  a  rare  contingency ;  for  it  has  been  observed,  by 
more  than  one  paleontologist,  that  very  thick  deposits  are 
usually  barren  of  organic  remains,  except  near  their  upper  or 
lower  limits. 

It  would  seem  that  each  separate  formation,  like  the  whole 
pile  of  formations  in  any  country,  has  generally  been  intermit- 
tent in  its  accumulation.  When  we  see,  as  is  so  often  the  case, 
a  formation  composed  of  beds  of  dilVercnt  mineralogical  com- 
position, we  may  reasonably  suspect  that  the  jirocess  of  deposi- 
tion has  been  much  intcrnij)t(Ml,  as  a  change  in  the  currents  of 
the  sea,  and  a  supply  of  sediment  of  a  different  nature  will 
generally  have  been  due  to  geographical  changes  requiring 
much  time.  Nor  will  the  closest  ins]iection  of  a  formation  give 
any  idea  of  the  time  which  its  deposition  has  consumed.  Many 
instances  could  be  given  of  beds  only  a  few  feet  in  thickness, 


riiAr.  IX.  IN  ANY   SINGLE   FORMATION.  ogj 

roiM(\scntIiig  formations,  elsewhere  thousands  of  feet  in  thick- 
ness, and  which  must  have  required  an  enormous  period  for 
(heir  accumuhition  ;  yet  no  one  ignorant  of  this  fact  woukl  have 
snspecled  the  vast  lapse  of  time  represented  by  the  thinner  for- 
mation. Many  cases  could  be  f]fiven  of  the  lower  beds  of  a 
formation  havin*^  been  upraised,  denuded,  submcrj^ed,  and  then 
i('-covercd  by  the  upper  beds  of  the  same  formation — facts, 
shcnving  what  wide,  yet  easily-overlooked,  intervals  have  oc- 
curred in  its  accumulation.  In  other  cases  we  have  the  plainest 
evidence  in  great  fossilized  trees,  still  standing  upright  as  they 
grew,  of  many  long  intervals  of  time  and  changes  of  level 
(luring  the  process  of  deposition,  which  would  never  even  have 
been  suspected,  had  not  the  trees  chanced  to  have  been  pre- 
served :  tluis  Sir  C  Lyell  and  Dr.  Dawson  found  carboniferous 
beds  1,400  feet  tliick  in  Nova  Scotia,  with  ancient  root-bearing 
strata,  one  above  the  other,  at  no  less  than  sixty-eight  diiferent 
levels.  Hence,  when  the  same  species  occur  at  the  bottom, 
middle,  and  top  of  a  formation,  the  probability  is  that  they  have 
not  lived  on  the  same  spot  during  the  whole  period  of  depo- 
sition, but  have  disappeared  and  reapj)eared,  perhaps  many 
times,  during  the  same  geological  period.  So  that,  if  such  spe- 
cies were  to  undergo  a  consid(n-al)le  amount  of  modification 
during  any  one  geological  period,  a  section  would  not  include 
all  the  fin(^  intermediate  gradations  which  must  on  our  theory 
have  existed  between  them,  but  aljrupt,  though  perhaps  slight, 
changes  of  form. 

It  is  all-important  to  remember  that  natin-alists  have  no 
golden  rule  by  which  to  distinguish  species  and  varieties  ;  they 
grant  some  little  variability  to  each  species,  but  when  they 
meet  with  a  somewhat  greater  amount  of  dilference  between 
any  two  forms,  they  rank  both  as  species,  uidess  tliey  are  en- 
abled to  coimect  them  together  by  the  closest  intermediate 
gradations.  And  this  from  the  reasons  just  assigned  we  can 
seldom  hope  to  effect  in  any  one  geological  section.  Supposing 
B  and  C  to  b(;  two  sjiecies,  and  a  third.  A,  to  l)e  found  in  an 
older  and  underlying  bed;  even  if  A  were  strietly  intermediate 
l)(!tween  B  and  C,  it  would  simply  be  ranked  as  a  tliird  and 
distinct  sjiecies,  unl(\ss  at  the  sam«;  time  it  could  be  most 
closely  coimected  with  either  one  or  l)oth  forms  1)>'  intermediate 
varieties.  Nor  should  it  be  forgotten,  as  before  explaitied,  that 
A  might  ])(;  the  actual  ]irogenitor  of  B  and  C,  and  yet  might 
not  necessarily  be  strictly  intermediate  between  them  in  all  re- 
opccts.     So  that  we  might  obtain  the  parcnt>specics  and  its 


282  ABSENCE  OF  INTERMEDIATE  VAEIETIP:S      Chap.  IX. 

several  modified  descendants  from  tlu^  lower  and  upper  beds  of 
the  same  formation,  and  unless  "\ve  obtained  numerous  transi- 
tional gradations,  we  should  not  reco^ize  their  blood-relation- 
ship, and  should  consequently  be  compelled  to  rank  them  as 
distinct  species. 

It  is  notorious  on  what  excessively  slight  differences  many 
paleontologists  liave  founded  their  species;  and  they  do  this 
the  more  readily  if  the  specimens  come  from  different  sub- 
stages  of  the  same  formation.  Some  experienced  conchologists 
are  now  sinking  many  of  the  very  fine  species  of  D'Orbigny 
and  others  into  the  rank  of  varieties ;  and  on  this  view  we  do 
find  the  kind  of  evidence  of  change  which  on  tlie  theory  we 
ought  to  find.  Look,  again,  at  the  later  tertiary  deposits, 
which  include  many  shells  believed  by  the  majority  of  natural- 
ists to  be  identical  with  existing  species ;  but  some  excellent 
naturalists,  as  Agassiz  and  Pictet,  maintain  that  all  these  ter- 
tiary species  are  specifically  distinct,  though  the  distinction  is 
admitted  to  be  very  slight ;  so  that  here,  unless  we  believe  that 
these  eminent  naturalists  have  been  misled  by  their  imaginations, 
and  that  these  late  tertiary  species  really  present  no  difference 
whatever  from  their  living  representatives,  or  unless  we  believe 
that  the  great  majority  of  naturalists  are  wrong,  and  that  the 
tertiar}'  sjiecies  are  all  truly  distinct  from  the  recent,  we  have 
evidence  of  the  frequent  occurrence  of  sliglit  modifications  of 
the  kind  required.  If  we  look  to  rather  wider  intervals  of  time, 
namely,  to  distinct  but  consecutive  stages  of  the  same  great 
formation,  we  find  that  the  embedded  fossils,  though  almost 
universally  ranked  as  specifically  different,  yet  are  far  more 
closely  related  to  each  other  than  are  the  species  found  in  more 
widely-separated  formations ;  so  that  here  again  we  have  un- 
doubted evidence  of  change  in  the  direction  required  by  the 
theory ;  but  to  this  latter  subject  I  shall  have  to  return  in  the 
following  chapter. 

With  animals  and  plants  that  propagate  rapidly  and  do 
not  wander  much,  there  is  reason  to  suspect,  as  we  have  for- 
merly seen,  that  their  varieties  are  generally  at  first  local ;  and 
that  such  local  varieties  do  not  spread  widely  and  supplant 
their  parent-forms  imtil  they  have  been  modified  and  perfected 
in  some  considerable  degree.  According  to  this  A'icw,  the 
chance  of  discovering  in  a  fonnation  in  any  one  country  all  the 
early  stages  of  transition  between  any  two  such  forms  is  small, 
for  the  successive  changes  are  supposed  to  liave  been  local,  or 
confined  to  some  one  spot.     Most  marine  animals  have  a  wide 


Chap.  IX.  IN   ANY  SINGLE  FORMATION.  033 

range ;  and  wo  have  soon  tliat  with  plants  it  is  those  wliicli 
have  the  widest  rani>-o,  that  oftonest  present  varieties;  so  that, 
witli  shells  and  other  marine  animals,  it  is  pro])able  that  those 
which  liavc  had  the  widest  range,  far  exceeding  the  limits  of 
the  known  geological  formations  of  Europe,  have  oftcnest  given 
rise,  ilrst  to  local  varieties,  and  ultimately  to  new  species;  and 
this  again  would  greatly  lessen  the  chance  of  our  being  able 
to  trace  the  stages  of  transition  in  any  one  geological  for- 
mation. 

It  is  a  more  important  consideration,  leading  to  the  same 
result,  as  lately  insisted  on  by  Dr.  Falconer,  namely,  that  the 
period  during  which  each  species  underwent  modification, 
though  long  as  measured  by  years,  was,  from  the  reasons 
lately  assigned,  probably  short  in  comparison  with  that  during 
which  it  remained  without  undergoing  any  ch.ange. 

It  should  not  be  forgotten  that,  at  the  present  day,  with 
perfect  specimens  for  examination,  two  forms  can  seldom  be 
connected  by  intermediate  varieties,  and  thus  proved  to  be  the 
same  species,  initil  many  specimens  are  collected  from  many 
]ilaces ;  and,  in  tlie  case  of  fossil  species,  this  can  rarely  be 
effected  by  paleontologists.  "We  shall,  perhaps,  best  perceive 
the  improbability  of  our  being  enabled  to  connect  species  by 
numerous  fine,  intermediate  fossil  links,  by  asking  ourselves 
^^•hether,  for  instance,  geologists  at  some  future  period  will  be 
able  to  prove  that  our  different  breeds  of  cattle,  sheep,  horses, 
and  dogs,  are  descended  from  a  single  stock  or  from  several 
alwriginal  stocks;  or,  again,  Avhether  certain  sea-shells  inliabit- 
ing  the  shores  of  North  America,  which  are  ranked  by  some 
conchologists  as  distinct  species  from  their  European  represent- 
atives, and  by  other  conchologists  as  only  varieties,  are  really 
varieties,  or  are,  as  it  is  called,  specifically  distinct.  This  could 
be  effected  only  by  the  future  geologist  discovering  in  a  fossil 
state  numerous  intermediate  gradations  ;  and  such  success  is 
imj>r(>bable  in  tlu;  iiighest  degree. 

It  has  been  assorted  over  and  over  again,  l)y  Avritors  who 
believe  in  the  immutability  of  species,  that  geology  yields  no 
linking  forms.  This  assertion  is  entirely  erroneous.  As  Sir 
J.  Lubbock  has  nMuarkod,  "Every  species  is  a  link  between 
other  allied  forms."  We  clearly  see  this  if  we  take  a  genus 
having  a  score  of  recent  and  extinct  species  and  destroy  four- 
lifths  of  thorn  ;  for  in  tliis  case  no  one  doubts  that  the  ri'inain- 
dor  will  stand  much  more  distinct  from  each  other.  If  the  ex- 
treme forn)s  in  the  genus  happen  to  have  boon  thus  destroyed, 


284  ABSENCE  OF  INTERMEDIATE  VARIETIES      Chap.  IX. 

the  genus  itself  in  most  cases  will  stand  more  distinct  from 
ntlicr  allied  genera.  The  camel  and  the  pig,  or  the  horse  and 
the  tapir,  are  now  obviously  very  distinct  forms  ;  but  if  we  add 
the  several  fossil  quadrupeds  which  have  already  been  discov- 
ered to  the  families  including  the  camel  and  pig,  these  forma 
become  joined  by  links  not  extremely  wide  apart.  The  chain 
of  linking  forms  does  not,  hovrever,  in  these  cases,  or  in  any 
case,  run  straight  from  the  one  living  form  to  the  other,  but 
takes  a  circuitous  sweep  through  the  forms  which  lived  during 
long-past  ages.  What  geological  research  has  not  revealed, 
is  the  former  existence  of  infinitely  numerous  gradations,  as 
fine  as  existing  varieties,  connecting  nearly  all  our  existing 
species  w'itli  extinct  species.  But  this  ought  not  to  be  ex- 
pected ;  yet  this  has  been  repeatedly  advanced  as  a  most 
serious  objection  against  my  views. 

It  may  be  worth  while  to  sum  up  the  foregoing  remarks  on 
the  causes  of  the  imperfection  of  the  geological  record  under 
an  imaginary  illustration.  The  Malay  Archipelago  is  about 
the  size  of  liluvopc  from  the  North  Cape  to  the  Mediterranean, 
and  fi'om  Britain  to  Russia ;  and  therefore  equals  all  the  geo- 
logical formations  which  have  been  examined  with  any  accu- 
racy, excepting  those  of  the  United  States  of  America.  I  fully 
agree  with  Mr.  Godwin-x^usten,  that  the  present  condition  of 
the  Malay  Archipelago,  with  its  numerous  large  islands  sep- 
arated by  wide  and  shallow  seas,  probably  represents  the  for- 
mer state  of  Europe,  while  most  of  our  formations  were  accu- 
mulating. The  Malay  Archipelago  is  one  of  the  richest  re- 
gions of  the  "whole  world  in  organic  beings ;  yet,  if  all  the 
species  were  to  be  collected  which  have  ever  lived  there,  how 
imperfectly  would  they  represent  the  natural  history  of  the 
world ! 

But  Ave  have  every  reason  to  believe  that  the  terrestrial 
productions  of  the  archipelago  would  be  preserved  in  an  ex- 
tremely imperfect  manner  in  the  formations  which  we  suppose 
to  be  there  accumulating.  Not  many  of  the  strictly  littoral 
animals,  or  of  those  Avhich  lived  on  naked  submarine  rocks, 
would  be  embedded ;  and  those  embedded  in  gravel  or  sand 
would  not  endure  to  a  distant  epoch.  Wherever  sediment  did 
not  accumulate  on  the  bed  of  the  sea,  or  where  it  did  not  accu- 
mulate at  a  sufficient  rate  to  protect  organic  bodies  from  decay, 
no  remains  could  be  preserved. 

Formations  rich  in  fossils  of  many  kinds,  and  of  thick- 
ness sufficient   to   last  to   an   age   as  distant   in   futurity  as 


Chap.  IX.  IN   ANY  SINGLE  FORMATION.  285 

the  secondary  formations  lie  in  the  past,  -wonkl  f^cncrally 
be  formed  in  the  archipehigo  only  during  poriods  of  subsi- 
dence. These  periods  of  subsidence  would  be  separated 
from  each  other  by  immense  intervals  of  time,  during  which 
the  area  would  be  either  stationary  or  rising  ;  while  rising, 
the  fossiliferous  formations  on  the  sleeper  shores  would  be 
destroyed,  almost  as  soon  as  accumulated,  by  the  incessant 
coast-action,  as  we  now  see  on  the  shores  of  South  America ; 
even  throughout  the  extensive  and  shallow  seas  witiiin  the 
archipelago  sedimentary  beds  could  hardly  be  accumulated 
of  great  thickness  during  the  periods  of  elevation,  or  become 
capped  and  protected  by  subsequent  deposits,  so  as  to  have 
a  good  chance  of  enduring  to  a  very  distant  future.  During 
the  periods  of  subsidence,  there  would  probably  be  much  ex- 
tinction of  life ;  during  the  periods  of  elevation,  there  would 
be  much  variation,  but  the  geological  record  would  then  be 
least  perfect. 

It  may  be  doubted  whether  the  duration  of  any  one 
great  period  of  subsidence  over  the  whole  or  part  of  the 
archipelago,  together  with  a  contemporaneous  accumulation 
of  sediment,  would  exceed  the  average  duration  of  the  same 
specific  forms;  and  these  contingencies  are  indispensable  for 
the  preservation  of  all  the  transitional  gradations  between 
any  two  or  more  species.  If  such  gradations  were  not  all 
fully  preserved,  transitional  varieties  would  merely  appear 
as  so  many  new  and  distinct  species.  It  is  also  probable 
that  each  great  period  of  subsidence  would  be  interrupted 
by  oscillations  of  level,  and  that  slight  climatal  changes 
would  intervene  during  such  lengthy  periods  ;  and  in  these 
cases  the  inhabitants  of  the  archipehigo  would  migrate,  and 
no  closely-consecutive  record  of  their  modifications  could  be 
preserved  in  any  one  formation. 

Very  many  of  the  marine  inhabitants  of  the  archipelago 
now  range:  thousands  of  miles  beyond  its  confines  ;  and 
analogy  plainly  leads  to  the  belief  that  it  would  be  chiefly 
these  far-ranging  species,  though  only  some  of  them,  which 
would  oftenest  produce  new  varieties  ;  and  the  varieties 
would  at  first  generally  be  local  or  confined  to  one  place ; 
but  if  jiossessed  of  any  decided  advantage,  or  when  further 
modified  and  improve<l,  they  would  slowly  spread  and  supplant 
their  parent-forms.  ^V^hen  such  varieties  returned  to  their 
ancient  homes,  as  they  would  difTcr  from  their  former  state, 
in  a  nearlv-unifonn,  though  ]>orhaj)s  extremely-slight  degree. 


280  SUDDEN  A^PEAPwA^X'E  OF  Chap.  IX, 

and  as  they  would  Ijc  found  embedded  in  sliglilly-different 
sub-stages  of  the  same  formation,  they  would,  according  to 
the  principles  followed  l)y  many  paleontologists,  be  ranked 
as  new  and   distinct   species. 

If,  then,  there  be  some  degree  of  truth  in  these  remarks, 
we  have  no  right  to  expect  to  find,  in  our  geological  for- 
mations, an  infinite  number  of  those  fine  transitional  forma 
which,  on  our  theor}',  have  connected  all  the  past  and  present 
species  of  the  same  gi-oup  into  one  long  and  branching 
chain  of  life.  We  ought  only  to  look  for  a  few  links,  and 
such  assuredly  Ave  do  find — some  more  distantly,  some  more 
closely,  related  to  each  other ;  and  these  links,  let  them  be 
ever  so  close,  if  found  in  different  stages  of  the  same  forma- 
tion, would,  by  many  paleontologists,  be  ranked  as  distinct 
species.  But  I  do  not  pretend  that  I  should  ever  have  suspect- 
ed how  poor  was  the  record  in  the  best  preserved  geologi- 
cal sections,  had  not  the  absence  of  innumerable  transitional 
links  between  the  species  which  lived  at  the  commencement 
and  close  of  each  formation,  pressed  so  hardly  on  my  theory. 

On  the  sudden  Apjjearance  of  ichole   Groups  of  allied 
/Species. 

The  abrupt  manner  in  which  Avhole  groups  of  species 
suddenly  appear  in  certain  formations,  has  been  urged  by 
several  paleontologists — for  instance,  by  Agassiz,  Pictet,  and 
Sedgwick — as  a  fatal  objection  to  the  belief  in  the  trans- 
mutation of  species.  If  numerous  species,  belonging  to  the 
same  genera  or  families,  have  really  started  into  life  at 
once,  the  fact  would  be  fatal  to  the  theory  of  descent  with 
slow  modification  through  natural  selection.  For  the  devel- 
opment of  a  group  of  forms,  all  of  which  have  descended 
from  some  one  progenitor,  nuist  have  been  an  extremely  slow 
process;  and  the  progenitors  must  have  lived  long  ages 
before  their  mothfied  descendants.  But  we  continually  over- 
rate the  perfection  of  the  geological  record  and  falsely  infer, 
because  certain  genera  or  families  have  not  been  foimd 
beneath  a  certain  stage,  that  they  did  not  exist  before  that 
stage.  In  all  cases  positive  paleontological  evidence  may 
be  implicitly  trusted  ;  negative  evidence  is  worthless,  as 
experience  has  so  often  sho"wn.  We  continually  forget  how 
large  the  world  is,  compared  with  the  area  over  which  our 
geological    formations    have    been    carefully    examined  ;    we 


CiiAP.  IX.  GROUPS  OF  ALLIED  SPECIES.  287 

forf^ot  that  g-ioups  of  species  may  elsewhere  have  long: 
existed,  and  liavc  slowly  multiplied,  before  they  invaded 
the  ancient  archipela^^oes  of  Europe  and  the  United  States. 
We  do  not  make  due  allowance  for  the  enormous  intervals 
of  time  which  have  elapsed  between  our  consecutive  forma- 
tions— loiiocr  perhaps  in  many  cases  than  the  time  required 
for  the  accumulation  of  each  formation.  These  intervals 
will  have  g-iven  time  for  the  multiplication  of  species  from 
some  one  or  some  few  parent-forms ;  and  in  the  succeeding^ 
formation  such  groups  of  species  will  appear  as  if  suddenly 
created. 

I  may  here  recall  a  remark  formerly  made,  namely,  that 
it  might  require  a  long  succession  of  ages  to  adapt  an  or- 
ganism to  some  new  and  peculiar  line  of  life,  for  instance, 
lo  liy  through  the  air;  and  consequently  that  the  transition- 
al forms  would  often  remain  confined  to  some  one  region  ; 
but  that,  when  this  adaptation  had  once  been  effected,  and 
a  few  species  had  thus  acquired  a  great  advantage  over 
other  organisms,  a  comparatively  short  time  would  1)0  neces- 
sary to  produce  many  divergent  forms,  ■which  would  spread 
rapidly  and  widely  throughout  the  world.  Prof.  Pictet, 
in  his  excellent  review  of  this  work,  in  commenting  on 
early  transitional  forms,  and  taking  birds  as  an  illustration, 
cannot  see  how  the  successive  modifications  of  the  ante- 
rior limbs  of  a  supposed  protot\'pe  could  possibly  have  been 
of  any  advantage.  But  look  at  the  penguins  of  the  Southern 
Ocean;  have  not  these  birds  their  front  limbs  in  this  precise 
intermediate  state  of  "neither  true  arms  nor  true  wings?" 
Yet  these  birds  hold  their  place  victoriously  in  the  battle 
for  life;  for  they  exist  in  infinite  numbers  and  of  many  kinds. 
I  do  not  suppose  that  we  here  see  the  real  transitional 
grades  through  which  the  wings  of  birds  have  passed ;  but 
what  special  dilliculty  is  there  in  believing  that  it  might 
profit  the  modified  descendants  of  the  ]ienguin,  first  to  become 
enabled  to  flap  along  the  surface  of  the  sea  like  the  logger- 
headed  duck,  and  ultimately  to  rise  from  its  surface  and  glide 
through  the  air? 

I  will  now  give  a  fmv  examples  to  illustrate  the  fore- 
going remarks,  and  to  show  how  liable  we  are  to  error  in 
supposing  that  whole  groups  of  sj^ecies  have  suddenly  been 
produced.  Even  in  so  short  an  interval  as  that  between  the 
iirst  and  second  editions  of  Pictet's  great  work  on  Paleon- 
tologv,  pu])lished  in  18-i4-'4G  and  in  ISSS-^o?,  the  conclusions 


288  SUDDEN  AITEAEANCE  OF  Cuap.  IX. 

on  the  first  appearance  and  disappearance  of  several  groups 
of  animals  have  l)ocn  considerably  modified ;  and  a  third 
edition  •would  rociuire  still  further  changes.  I  may  recall 
the  ■well-known  fact  that  in  geological  treatises,  published 
not  many  years  ago,  mammals  were  always  spoken  of  as 
liaving  abruptly  come  in  at  the  commencement  of  the  tertiary 
series.  And  now  one  of  the  richest  known  accumulations  of 
fossil  mammals,  for  its  thickness,  belongs  to  the  middle  of 
the  secondary  series ;  and  true  mammals  have  been  discov- 
ered in  the  new  red  sandstone  at  nearly  the  commencement  of 
tliis  great  series.  Cuvier  used  to  urge  that  no  monkey  oc- 
curred in  any  tertiary  stratum  ;  but  now  extinct  species  have 
been  discovered  in  India,  South  America,  and  in  Europe,  as  far 
back  as  the  miocene  stage.  Had  it  not  been  for  the  rare  acci- 
dent of  the  preservation  of  footsteps  in  the  new  red  sandstone 
of  the  United  States,  who  would  have  A^entured  to  suppose 
that,  besides  reptiles,  no  less  than  at  least  thirty  kinds  of  birds, 
some  of  gigantic  size,  existed  during  that  period  ?  Not  a  frag- 
ment of  bone  has  been  discovered  in  these  beds.  Notwith- 
standing that  the  number  of  joints  shown  in  the  fossil  impres- 
sions corresponds  with  the  number  in  the  several  toes  of  living 
birds'  feet,  some  authors  doubt  whether  the  animals  which  left 
these  impressions  were  really  birds.  Until  quite  recently  these 
authors  might  have  maintained,  and  some  have  maintained,  that 
the  whole  class  of  birds  came  suddenly  into  existence  during 
the  eocene  period;  but  now  we  know,  on  the  authority  of 
Prof.  Owen,  that  a  bird  certainly  lived  during  the  deposition 
of  the  upper  greensand  ;  and  still  more  recently,  that  strange 
bird,  the  ArchcopterA'x,  with  a  long,  lizard-like  tail,  bearing  a 
pair  of  feathers  on  each  joint,  and  with  its  wings  furnished  with 
two  free  claAvs,  has  been  discovered  in  the  oolitic  slates  of  So- 
Icnhofcn.  Hardly  any  recent  discovery  shows  more  forcibly 
than  this,  how  little  we  as  yet  know  of  the  former  inhabitants 
of  the  Avorld. 

I  may  give  another  instance,  which,  from  having  passed  im- 
der  my  own  eyes,  has  much  struck  me.  In  a  memoir  on  Fossil 
Sessile  Cirripedes,  I  have  stated  that,  from  the  large  number 
of  existing  and  extinct  tertiary  species  ;  from  the  extraordinary 
abundance  of  the  individuals  of  many  sj:)ecies  all  over  the  world, 
from  the  Arctic  regions  to  the  equator,  inhabiting  A-arious 
zones  of  depths  from  the  upper  tidal  limits  to  50  fathoms ;  from 
the  perfect  manner  in  which  specimens  are  preserved  in  the 
oldest  tertiary  beds  ;  from  the  case  with   which  even  a  frag- 


Chap.  IX.  GROUPS  OF  ALLIED  SPECIES.  289 

nicnt  of  a  valve  can  be  recorrnizetl ;  from  all  these  circum- 
stances, I  infer  that,  had  sessile  cirripcdes  existed  durinn^  the 
secondary  periods,  they  would  certainly  have  Ijcen  preserved  and 
discovered  ;  and  as  not  one  species  had  then  been  discovered  in 
oeds  of  this  age,  I  concluded  that  this  grcjit  jrroup  had  been 
suddenly  develo])ed  at  the  commencement  of  the  tertiary  series. 
This  was  a  sore  trouble  to  me,  adding  as  I  thought  one  more 
instance  of  the  abrupt  appearance  of  a  great  group  of  species. 
But  my  work  had  hardly  been  published,  when  a  skilful  pale- 
ontologist, M.  Bosquet,  sent  me  a  drawing  of  a  perfect  speci- 
men of  an  unmistakable  sessile  cirripede,  Avhich  he  had  him- 
self extracted  from  the  chalk  of  Belgium.  And,  as  if  to  make 
tlio  case  as  striking  as  possil)le,  this  sessile  ciiripede  was  a 
C'hthamalus,  a  very  common,  large,  and  ubiquitous  genus,  of 
which  not  one  specimen  has  as  yet  been  foimd  even  in  any  ter- 
tiary stratum.  Hence  we  now  positively  know  that  sessile 
cirripedes  existed  during  the  secondary  period  ;  and  these  cir- 
ripcdes might  have  been  the  progenitors  of  our  many  tertiary 
and  existhig  species.  Still  more  recently  Tyrgoma  has  been 
discovered  by  Mr,  AA'oodward  in  the  upper  chalk. 

The  case  most  frecjucntly  insisted  on  by  paleontologists  of 
the  apparently  sudden  appearance  of  a  whole  group  of  species, 
is  that  of  the  teieostean  iishes,  low  down  in  the  Chalk  period. 
This  group  includes  the  large  majority  of  existing  species. 
Lately,  Prof.  Pictet  has  carried  their  existence  one  sub-stage 
further  back ;  and  some  paleontologists  believe  that  certain 
nmch  older  fishes,  of  which  the  affinities  are  as  yet  imperfectly 
known,  are  really  teieostean.  Assuming,  however,  that  the 
whole  of  them  did  appear,  as  Agassiz  maintains,  at  the  com- 
mencement of  the  chalk  formation,  the  fact  would  certainly  be 
highly  remarkal)lc ;  but  I  cannot  see  that  it  would  be  an  in- 
superalile  objection  to  these  views,  unless  it  could  likewise  be 
shown  that  tlie  species  of  this  group  appeared  suddenly  and 
simultaneously  throughout  the  world  at  tliis  same  period.  It 
is  almost  superfluous  to  remark  that  hardly  an}'  fossil-lish  are 
known  from  south  of  the  equator;  and  by  running  tlu-ougli 
Pictet's  Paleontology  it  will  be  seen  that  very  few  species  are 
Ivtiown  from  several  formations  in  Europe.  Some  few  families 
of  (ish  now  have  a  confined  range ;  the  teieostean  fish  miglit 
formerly  have  had  a  simihirly  confined  range,  and  after  having 
been  largely  developed  in  some  one  sea,  might  have  spread 
widely.  Nor  have  we  any  right  to  suppose  that  the  seas  of 
the  world  have  always  been  so  freely  open  from  eouth  to  north 
13 


£90  GROUPS   OF  ALLIED  SPECIES  Cuap.  IX. 

as  they  are  at  present.  Even  at  tliis  day,  if  the  Malay  Archi 
pehigo  "svcre  converted  into  land,  the  tropical  parts  of  the  In- 
dian Ocean  would  form  a  large  and  perfectly-enclosed  basin, 
in  Avliich  any  great  group  of  marine  animals  might  be  multi- 
plied ;  and  here  they  would  remain  confined,  until  some  of  the 
species  became  adapted  to  a  cooler  climate,  and  were  enabled 
to  double  the  southern  capes  of  Africa  or  Australia,  and  thus 
reach  other  and  distant  seas. 

From  these  considerations,  from  our  ignorance  of  the  geol- 
ogy of  other  countries  beyond  the  confines  of  Europe  and  the 
United  States,  and  fi'om  the  revolution  in  our  paleontological 
knowledge  eflected  by  the  discoveries  of  the  last  dozen  years, 
it  seems  to  me  to  be  about  as  rash  to  dogmatize  on  the  succes- 
sion of  organic  forms  throughout  the  world,  as  it  would  be  for 
a  naturalist  to  land  for  five  minutes  on  a  barren  point  in  Aus- 
tralia, and  then  to  discuss  the  number  and  range  of  its  jjroduc- 
tions. 

On  the  sudden  A2)2)earance  of  Groups  of  allied  Species  in 
the  loicest  Jcnoicn  Fossil  if eroiis  Strata. 

There  is  another  and  allied  difficulty,  which  is  much  more 
serious.  I  allude  to  the  manner  in  Avhich  many  species  in  sev- 
eral of  the  main  divisions  of  the  animal  kingdom  suddenly 
appear  in  the  lowest  known  fossiliferous  rocks.  Most  of  the 
arguments  which  have  convinced  me  that  all  the  existing 
species  of  the  same  group  are  descended  from  a  single  pro- 
genitor, apply  with  nearly  equal  force  to  the  earliest  known 
species.  For  instance,  it  cannot  be  doubted  that  all  the  Silu- 
rian trilobites  are  descended  from  some  one  crustacean,  which 
must  have  lived  long  before  the  Silurian  age,  and  which  prob- 
ably difl'ered  greatly  from  an>'  known  animal.  Some  of  the 
most  ancient  Silurian  animals,  as  the  Nautilus,  Lingula,  etc., 
do  not  difter  much  from  living  sjiccies;  and  it  cannot  on  our 
theory  be  sujiposed  that  these  old  species  were  the  progenitors 
of  all  the  species  belonging  to  the  same  groups  whicli  have 
subseciucntly  appeared,  for  they  are  not  in  any  degree  inter- 
mediate in  character. 

Consequently,  if  the  tlicory  be  true,  it  is  indis]nitable 
that,  before  the  lowest  Silurian  or  Cambrian  stratum  was  do- 
posited  long  periods  elapsed,  as  long  as,  or  probably  far  longer 
than,  tlie  whole  interval  from  the  Cambrian  age  to  the  present 
day;  I'.nd  that  during  these  vast  periods  the  world  swarmed 


CuAP.  IX.  IN  LOWEST  FOSSILIFEROUS  STRATA.  ogj 

■\vitli  livinp;  creatures.  Here  we  encounter  a  formidable  objec- 
tion ;  for  it  sceins  dou])tful  whether  the  eartli  in  a  lit  state  for 
the  habitation  of  livin"^  creatures  has  lasted  lono;  cnouo-h.  Sir 
W.  Tiionipson  concludes  that  the  consolidation  of  the  crust  can 
hardly  have  occurred  less  than  20  or  more  than  400  million 
years  ago,  Ijut  probably  not  less  than  98  or  more  than  200  mill- 
ion years.  Tliese  very  wide  limits  show  how  doubtful  the 
data  are  ;  and  other  elements  may  have  to  be  introduced  into 
tlie  problem.  Mr.  C'roll  estimates  that  about  00  million  years 
have  elapsed  since  the  Cambrian  period,  but  this,  judging  from 
the  small  amoiuit  of  organic  change  since  the  commencement 
of  the  Glacial  epoch,  seems  a  very  short  time  for  the  many  and 
great  mutations  of  life,  which  have  certainlv  occurred  since  the 
Cambrian  formation;  and  the  previous  140  million  years  can 
hardly  be  considered  as  sufficient  for  the  development  of  the 
varied  forms  of  life  which  certainly  existed  toward  the  close  of 
the  Cambrian  period.  It  is,  however,  probable,  as  Sir  ^\^ 
Thompson  insists,  that  the  world  at  a  verj-  early  period  was 
subjected  to  more  rapid  and  violent  changes  in  its  physical  con- 
ditions than  those  now  occurring;  and  such  changes  would 
have  led  to  corresponding  rapid  changes  in  the  organic  being-s 
which  inhabited  the  world  at  this  remote  period. 

To  the  question  why  we  do  not  hnd  rich  fossiliferous  de- 
posits belonging  to  these  assumed  earliest  periods,  I  can  give 
no  satisfactory  answer.  Several  eminent  geologists,  with  Sir 
li.  Murehison  at  their  head,  were  until  recently  convinced  that 
we  beheld  in  the  organic  remains  of  the  lowest  Silurian  stratum 
the  first  dawn  of  life.  Other  highly-competent  judges,  as  Ja-qM 
and  E.  Forbes,  have  disputed  this  conclusion.  We  should  not 
forget  that  only  a  small  jiortion  of  the  world  is  known  with  ac- 
curacy. Not  long  ago,  M.  Barrande  added  another  and  lower 
stage,  abounding  with  new  and  peculiar  species  beneath  the 
old  Silurian  system.  Henmants  of  several  forms  have  also 
been  detected  beneath  BaiTande's  so-called  primordial  zone  in 
the  Longmynd  group,  now  divided  into  two  stages,  and  con- 
stituting the  Lower  Cambrian  system.  The  presence  also  of 
])hosphatie  nodules  and  bitunnnous  matter  in  some  of  the  low- 
est azoic  rocks,  jirobably  indicates  life  at  these  periods.  Now 
the  great  discovery  of  the  Eozoon  in  the  Laurent ian  f(jrmation 
of  Canada  has  been  made,  for,  after  reading  Dr.  Carpenter's 
description  of  tliis  fossil,  it  is  scarcely  possible  to  doubt  regard- 
ing its  organic  nature.  There  are  tiiree  great  series  of  strata 
beneath  tiie  Siluriiin  svslein  in  Canad:i,  in  the  lowest  of  which 


292  GROUPS   OF  ALLIED  SPECIES  Chap.  IX. 

the  Eozoon  was  found ;  and  Sir  W.  Logan  states  that  their 
"  united  thickness  may  jiossibly  far  surpass  that  of  all  the  suc- 
ceeding rocks,  fiom  llie  base  of  the  paleozoic  series  to  the  pres- 
ent time.  We  arc  thus  carried  back  to  a  period  so  remote, 
that  the  appearance  of  the  so-called  Primordial  fauna  (of 
Barraudc)  may  by  some  be  considered  as  a  comparatiyely 
modern  eyent."  The  Eozoon  belongs  to  the  most  lowly  or- 
ganized of  all  classes  of  animals,  but  for  its  class  is  highly  organ- 
ized ;  it  existed  in  countless  numbers,  and,  as  Dr,  Dawson  has  re- 
marked, certainly  preyed  on  other  minute  organic  beings,  which 
must  have  lived  in  great  numbers.  Thus  the  words,  which  I 
wrote  in  1859,  about  the  vast  periods  which  had  probably 
elapsed  before  the  Cambrian  system,  are  almost  the  same  with 
those  since  used  by  Sir  W.  Logan.  Nevertheless,  the  difliculty 
of  assigning  any  good  reason  for  the  absence  beneath  the  up- 
per Cambrian  formations  of  vast  piles  of  strata  rich  in  fossils, 
is  very  great.  It  does  not  seem  probable  that  the  most  an- 
cient beds  have  been  quite  worn  away  by  denudation,  or  that 
their  fossils  have  been  wholly  obliterated  liy  raetamorphic  ac- 
tion, for  if  this  had  been  the  case  we  should  have  found  only 
small  remnants  of  the  formations  next  succeeding  them  in  age, 
and  these  -would  always  have  existed  in  a  partially-metamor- 
])hoscd  condition.  But  the  descriptions  which  we  possess  of 
the  Silurian  deposits  over  immense  territories  in  Russia  and  in 
North  America,  do  not  support  the  view,  that  the  older  a  for- 
mation is,  the  more  it  has  invariably  suffered  extreme  denuda- 
tion and  metamorphism. 

The  case  at  present  must  remain  inexplicable ;  and  may  be 
truly  urged  as  a  valid  argument  against  the  views  here  enter- 
tained. To  show  that  it  may  hereafter  receive  some  explana- 
tion, I  will  give  the  following  hypothesis  :  From  the  nature  ot 
the  organic  remains  which  do  not  appear  to  have  inhabited 
profound  depths,  in  the  several  formations  of  Europe  and  of 
the  United  States;  and  from  the  amount  of  sediment,  miles  in 
thickness,  of  Avhich  the  formations  arc  composed,  we  may 
infer  that  from  first  to  last  large  islands  or  tracts  of  land, 
whence  the  sediment  was  derived,  occurred  in  the  neighbor- 
hood of  the  now  existing  continents  of  Europe  and  North 
America.  But  we  do  not  know  what  Avas  the  state  of  tilings 
in  the  intervals  between  the  several  successive  fonnations ; 
whether  Europe  and  the  United  States  during  these  intervals 
existed  as  dry  land,  or  as  a  submarine  surface  near  land,  on 
which  sediment  was  not  deposited,  or  as  the  bed  of  an  open 
a  lid  unfathomable  sea. 


Chap.  IX.  IN  LOWEST  FOSSILIFEROUS  STRATA.  293 

Lookinp^  lo  the  existing  oceans,  whicli  are  thrice  as  exten- 
sive as  the  hind,  we  see  them  studded  with  many  ishmds ;  but 
not  one  truly  oceanic  ishind  (with  the  exception  of  New  Zea- 
hind,  if  this  can  be  called  a  truly  oceanic  island)  is  as  ^-^et  known 
to  afford  even  a  renmant  of  any  jialeozoic  or  secondary  forma- 
tion. Hence  we  may  perhaps  infer  that,  duriufr  the  paleozoic 
and  secondary  periods,  neither  continents  nor  continental  islands 
existed  where  our  oceans  now  extend  ;  for  had  they  existed, 
])aleozoicand  secondary  formations  would  in  all  j)roi)ability  have 
been  accumulated  from  sediment  derived  from  their  wear  and 
tear ;  and  these  would  have  been  at  least  partiall}'  upheaved 
by  the  oscillations  of  level,  which  must  have  intervened  during 
these  enormousl3'-long'  periods.  If,  then,  we  may  infer  any 
thing  from  these  facts,  we  may  infer  that,  where  our  oceans 
now  extend,  oceans  have  extended  from  the  remotest  period  of 
which  we  have  any  record ;  and,  on  the  other  hand,  that  where 
cofitinents  now  exist,  large  tracts  of  hind  have  existc.'d,  subjected 
no  doubt  to  great  oscillations  of  level,  since  the  earliest  Silurian 
j)criod.  The  colored  map  appended  to  my  volume  on  Coral 
lleefs  led  me  to  conclude  that  the  great  oceans  are  still  mainly 
areas  of  subsidence,  the  great  archipelagoes  still  areas  of  oscil- 
lations of  level,  and  the  continents  areas  of  elevation.  IJut  we 
have  no  reason  to  assume  that  things  have  thus  remained  from 
the  beginning  of  the  world.  Our  continents  seem  to  have  been 
formed  by  a  jireponderance,  during  many  oscillations  of  level, 
of  the  force  of  elevation  ;  but  may  not  the  areas  of  preponder- 
ant movement  have  changed  in  the  lapse  of  ages  ?  At  a  period 
long  antecedent  to  the  Silurian  epoch,  continents  may  have  ex- 
isted where  oceans  are  now  spread  out ;  and  clear  and  open 
oceans  may  have  existed  where  our  continents  now  stand.  Nor 
should  we  be  justilied  in  assuming  that  if,  for  instance,  the  bed 
of  the  Pacific  Ocean  were  now  converted  into  a  continent,  we 
shouUl  there  find  sedimentary  formations  in  a  recognizable  con- 
dition older  than  the  Silurian  strata,  suj^posing  such  to  have 
been  formerly  deposited;  for  it  might  well  happen  that  strata 
which  had  subsided  some  miles  nearer  to  the  centre  of  the 
earth,  and  which  had  been  pressed  on  by  an  enormous  weight 
of  superincumbent  water,  might  have  undergcme  far  more  met- 
amorphic  action  than  strata  Avhich  have  always  remained 
nearer  to  the  surface.  The  immense  areas  in  some  parts  of  the 
world,  for  instance  in  South  America,  of  naked  metamorphic 
rocks,  which  must  have  been  heated  under  great  pressure,  have 
always  seemed  to  me  to  require  some  special  explanation;  and 


294  liirEEFECTION  OF  GEOLOGICAL  RECOED.     Chap.  L\. 

we  ma}'  pcrliaps  believe  that  avc  sec,  in  these  large  areas,  the 
many  formations  long  anterior  to  the  Silurian  epoch  in  a  com- 
pletely metamorphosed  and  denuded  condition. 

The  several  difficulties  here  discussed — namely,  that,  though 
•\vc  find  in  our  geological  formations  many  links  between  the 
species  which  now  exist  and  which  formerly  existed,  we  do  not 
find  infiiutely  numerous  fine  transitional  forms  closely  jouiing 
them  all  together;  the  sudden  manner  in  which  several  whole 
groups  of  species  first  appear  in  our  European  formations ; 
the  almost  entire  absence,  as  at  present  known,  of  formations 
rich  in  fossils  beneath  the  Cambrian  strata,  are  all,  undoubted- 
ly, of  the  most  serious  nature.  A\'e  see  this  in  the  fact  that 
tlie  most  eminent  paleontologists — namely,  CuA-ier,  Agassiz, 
Barrande,  Pictet,  Falconer,  E,  Forbes,  etc.,  and  all  our  great- 
est geologists,  as  Lyell,  IMurchison,  Sedgwick,  etc.,  have  unan- 
imously, often  vehemently,  maintained  the  immutability  of 
species.  But  Sir  Charles  Lyell  now  gives  the  support  of  his 
high  authority  to  the  opposite  side;  and  most  other  geologists 
and  paleontologists  are  much  shaken  in  their  former  belief. 
Those  who  believe  that  the  geological  record  is  in  any  d(>gree 
perfect,  will  undoubtedly  at  once  reject  the  theory.  For  my 
part,  following  out  Lyell's  metaphor,  I  look  at  the  geological 
record  as  a  history  of  the  world  imperfectly  kept,  and  written 
in  a  changing  dialect ;  of  this  history  we  possess  the  last  vol- 
ume alone,  relating  only  to  two  or  three  countries.  Of  this 
volume,  only  here  and  there  a  short  chapter  has  been  pre- 
served; and  of  each  page,  only  here  and  there  a  few  lines. 
Each  word  of  the  slowly-changing  language,  more  or  less  dif- 
ferent in  the  successive  chapters,  may  represent  the  forms  of 
life,  which  arc  entombed  in  our  consecutive  formations,  and 
which  falsely  appear  to  us  to  have  been  abruptl}'  introduced. 
On  this  vicAV,  the  difficulties  above  discussed  are  greatly  dimin- 
ished, or  even  disappear. 


CHAr.  X.  GEOLOGICAL  SUCCESSION.  295 


CHAPTER   X. 

ON   TUE   GEOLOGICAL   SUCCESSION   OF   ORGA^^C   BEINGS. 

On  the  Slow  nnd  Snccci>9ivc  Appearance  of  New  Species— On  their  Diflfcrcnt  Rates 
of  t'haii;,'C— Species  once  lost  do  not  reappear — Groui)8  of  Species  follow  the 
game  (Jc-ncnil  Rules  in  their  Appearance  and  Uisappearunce  as  do  Sinfrlc  Species 
— On  Extinction— On  Sininltaneoiis  C'hnn;,'es  in  the  Forms  of  Life  throu^rhout 
the  World— On  the  Affinities  of  Extinct  Species  to  cacli  other  and  to  Li\  in;;  Spe- 
cies—On the  State  of  Develo[)nKiit  of  Ancient  Forms— On  the  Succession  of  tho 
same  Typea  within  the  same  Areas- Summary  of  preccdinjj  and  present  Chapter. 

Let  us  now  see  whether  the  several  facts  and  laws  relatint^ 
to  the  geological  succession  of  organic  beings  better  accord 
with  the  common  view  of  the  immutability  of  species,  or  with 
that  of  their  slow  and  gradual  modification,  through  descent 
and  natural  selection. 

New  species  have  appeared  very  slowly,  one  after  another, 
both  on  the  land  and  in  the  waters.  Lyell  has  shown  that  it 
is  hardly  possible  to  resist  the  evidence  on  this  head  in  the 
case  of  the  several  tertiary  stages ;  and  every  year  tends  to  fill 
up  the  blanks  between  the  stages,  and  to  make  the  percentage 
system  of  lost  and  new  forms  more  gradual.  In  some  of  the 
most  recent  beds,  though  undoubtedly  of  high  antitjuity  if 
measured  by  years,  only  one  or  two  species  arc  extinct,  and 
only  one  or  two  arc  new,  having  appeared  there  for  the  first 
time,  either  locally,  or,  as  far  as  we  know,  on  the  face  of 
the  cartli.  The  secondary  formations  are  more  broken ;  but, 
as  Bronn  has  remarked,  neither  the  appearance  nor. disappear- 
ance of  the  many  extinct  species  embedded  in  each  formation 
has  been  simultaneous. 

Species  of  different  genera  iind  classes  have  not  changed 
at  the  same  rate,  or  in  the  same  degree.  In  the  older  tertiary 
beds  a  few  living  shells  may  still  be  foimd  in  the  midst  of  a 
multitude  of  extinct  fonns.  Falconer  has  given  a  striking  in- 
stance of  a  similar  fact,  for  an  existing  crocodile  is  associated 
with  many  lost  mammals  and  reptiles  in  the  sub-IIimalayan 
deposits.     The    Silurian   Liiigula    dilTcrs    but  little    from    the 


296  TJIE  GEOLOGICAL  SUCCESSION  Chap.  X. 

livinfj:  spocics  of  this  p^'onus ;  whereas  most  of  the  other  Silu- 
rian Molhiscs  and  all  the;  Crustaceans  have  changed  greatly. 
The  productions  of  the  land  seem  to  change  at  a  quicker  rate 
than  those  of  the  sea,  of  whicli  a  striking  instance  has  lately 
been  observed  in  Switzerland,  There  is  some  reason  to  believe 
that  organisms  high  in  the  scale,  change  more  quickly  than 
those  that  are  low ;  though  there  are  exceptions  to  this  rule. 
The  amount  of  organic  change,  as  Pictet  has  remarked,  is  not 
the  same  in  each  successive  so-called  formation.  Yet  if  we 
compare  any  but  the  most  closely-related  formations,  all  the 
species  will  be  found  to  have  undergone  some  change.  When 
a  species  has  once  disappeared  from  the  face  of  the  earth,  we 
have  no  reason  to  believe  that  the  same  identical  form  ever 
reappears.  The  strongest  apparent  exception  to  this  latter 
rule  is  that  of  the  so-called  "  colonies  "  of  JM.  Barrande,  which 
intrude  for  a  period  in  the  midst  of  an  older  formation,  and 
then  allow  the  preexisting  fauna  to  reappear ;  but  Lyell's  ex- 
jjlanation,  namely,  that  it  is  a  case  of  temporary  migration 
from  a  distinct  geographical  province,  seems  to  me  satisfac- 
tory. 

These  several  facts  accord  well  Avith  our  theory,  which  in- 
cludes no  fixed  law  of  development,  causing  all  the  inhabitants 
of  an  area  to  change  abruptl}^,  or  simultaneously,  or  to  an  equal 
degree.  Tlic  process  of  modification  must  be  slow,  and  will 
generally  affect  only  a  few  species  at  the  same  time  ;  for  the 
variability  of  each  species  is  quite  independent  of  that  of  all 
others.  Whether  such  variations  or  individual  differences  as 
may  arise  will  be  accumulated  through  natural  selection  in  a 
greater  or  less  degree,  thus  causing  a  greater  or  less  amount 
of  permanent  modification,  will  depend  on  many  complex  con- 
tingencies— on  the  variations  being  of  a  beneficial  nature,  on 
the  freedom  of  intercrossing,  on  the  slowly-changing  physical 
conditions  of  the  country,  on  the  immigration  of  new  colonists, 
and  on  the  nature  of  the  other  inhabitants  with  which  the 
varying  species  come  into  competition.  Hence  it  is  by  no 
means  surprising  that  one  species  should  retain  the' same  iden- 
tical form  much  longer  than  others  ;  or,  if  changing,  that  it 
should  chang(!  in  a  less  degree.  We  find  similar  relations  be- 
tween the  inhaljitants  of  distinct  countries  ;  for  instance,  the 
land-sliclls  and  coleopterous  insects  of  jNIadeira  have  come  to 
diller  considerably  from  their  nearest  allies  oh  the  continent 
of  l^^urope,  whereas  the  marine  shells  and  birtls  have  remained 
unaltered.    We  can  perhaps  understand  the  apparently  quicker 


Chap.  X.  OF  ORGANIC  BEINGS.  297 

rate  of  change  in  terrestrial  and  in  more  higlily-org'anized  pro- 
ductions compared  with  marine  and  lower  productions,  by  the 
more  complex  relations  of  tlie  hi<^her  beings  to  tlieir  organic 
and  inor^^nic  conditions  of  life,  as  explained  in  a  former  chap- 
ter. When  many  of  the  inhabitants  of  any  area  have  become 
modified  and  imjiroved,  we  can  imderstand,  on  the  principle  of 
competition,  and  from  tlie  all-important  relations  of  organism 
to  organism  in  the  struggle  for  life,  that  any  form  which  does 
not  become  in  some  deg'ree  modified  and  improved,  will  be 
liable  to  extermination.  Ilencc  we  see  why  all  the  species  in 
the  same  region  do  at  last,  if  we  look  to  long-enougli  intervals 
of  time,  become  niodilicd,  for  otherwise  they  would  become 
extinct. 

In  members  of  the  same  class  the  average  amount  of 
change,  during  long  and  equal  periods  of  time,  may,  perhaps,  be 
nearly  the  same  ;  but  as  the  accumulation  of  long'-enduring'  for- 
mations, rich  in  fossils,  depends  on  great  masses  of  sediment 
being  deposited  on  subsiding  areas,  our  formations  have  been 
almost  necessarily  accumulated  at  wide  and  irregularly  inter- 
mittent intervals  of  time  ;  consequently  the  amount  of  organic 
change  exhibited  by  the  fossils  embedded  in  consecutive  for- 
mations is  not  equal.  Each  formation,  on  this  view,  does  not 
mark  a  new  and  complete  act  of  creation,  but  only  an  occa- 
sional scene,  taken  almost  at  hazard,  in  an  ever  slowly-chan- 
ging drama. 

We  can  clearly  understand  why  a  species  when  once  lost 
should  never  reappear,  even  if  the  very  same  conditions  of  life, 
organic  and  inorganic,  should  recur.  For  thougli  the  offspring 
of  one  species  might  be  ada])t{Hl  (and  no  doubt  this  has  occurred 
in  innunieral)le  instances)  to  1111  the  place  of  another  species' in 
tlie  economy  of  Nature,  and  thus  supplant  it;  yet  the  two 
forms — the-  old  and  the  new — would  not  be  identically  th.e 
same  ;  for  both  would  almost  certainly  inherit  different  char- 
acters from  their  distinct  progenitors,  and  organisms  already 
differing  would  vary  in  a  different  manner.  For  instance,  it  is 
pist  possible,  if  all  our  fantail  jiigeons  were  destroyed,  that 
fanciers  might  make  a  new  breed  hardly  distinguishable  from 
tlie  present  breed  ;  but  if  the  parent  rock-pigeon  were  likewise 
destroyed,  and  imdcr  Nature  we  have  every  reason  to  believe 
that  j»arent-fonns  are  generallv  supplanted  and  exterminated 
bv  tlieir  improved  offspring,  it  is  incredible  that  a  fantail,  iden- 
tical with  th(!  existing  breed,  could  he  raised  from  any  other 
species  of  pigeon,  or  even  from  any  other  well-established  race 


298  GEOLOGICAL  SUCCESSION,  Chap.  X. 

of  the  domestic  pigeon,  for  the  successive  variations  would  al- 
most certainly  be  in  some  degree  different,  and  the  newly- 
formed  variety  would  probably  inherit  from  its  progenitor  some 
characteristic  differences. 

Groups  of  species,  that  is,  genera  and  families,  follow  the 
same  general  rules  in  their  appearance  and  disappearance  as 
do  single  s))ecies,  changing  more  or  less  qviickly,  and  in  a 
greater  or  lesser  degree.  A  group,  when  it  has  once  disap- 
peared, never  reappears ;  that  is,  its  existence,  as  long  as  it 
lasts,  is  contiruious.  I  am  aware  that  there  are  some  apparent 
excei:)tions  to  this  rule,  but  the  exceptions  are  surprisingly  few, 
so  few  that  E.  Forbes,  Pictet,  and  Woodward  (though  all 
strongly  opposed  to  such  views  as  I  maintain),  admit  its  truth ; 
and  the  rule  strictly  accords  with  the  theor}'.  For  all  the 
species  of  the  same  group,  however  long  it  may  have  lasted, 
are  the  modified  descendants  of  each  other,  and  of  some  com- 
mon progenitor.  In  the  genus  Lingula,  for  instance,  the 
species  which  have  successively  appeared  at  all  ages  nmst  have 
been  connected  by  an  unbroken  series  of  generations,  from  the 
loAvest  Silurian  stratum  to  the  present  day. 

We  have  seen  in  the  last  chapter  that  many  species  of  a 
group  sometimes  falsely  appear  to  have  come  in  abruptly  in  a 
body  ;  and  I  liavc  attempted  to  give  an  explanation  of  tliis 
fact,  which  if  true  would  be  fatal  to  my  views.  But  such  cases 
are  certainly  exceptional ;  the  general  rule  being  a  gradual  in- 
crease in  number,  until  the  group  reaches  its  maximum,  and 
then,  sooner  or  later,  a  gradual  decrease.  If  the  number  of 
the  species  included  within  a  genus,  or  the  number  of  the  gen- 
era Avithin  a  family,  be  represented  by  a  vertical  line  of  vary- 
ing thickness,  ascending  through  the  successive  geological  for- 
mations in  which  the  species  are  found,  the  line  will  sometimes 
falsely  appear  to  begin  at  its  lower  end,  not  in  a  sharp  point, 
but  al^ruptly ;  it  then  gradually  thickens  upward,  often  keep- 
ing for  a  space  of  equal  thickness,  and  xdtimately  thins  out  in 
the  upper  beds,  marking  the  decrease  and  final  extinction  of  the 
species.  This  gradual  increase  in  number  of  the  species  of  a 
group  is  strictly  conformable  Avith  the  theory,  for  the  species 
of  the  same  genus,  and  the  genera  of  the  same  family,  can  in- 
crease only  slowly  and  progressively ;  the  process  of  modifica- 
tion and  the  production  of  a  number  of  allied  forms  necessarily 
being  a  slow  and  gradual  process — one  species  first  giving 
rise  to  two  or  three  varieties,  these  being  slowly  converted  in- 
to specie?,  Avhich  in  their  turn  produce  by  equally  slow  steps 


Chap.  X.  EXTINCTION.  099 

other  varieties  and  species,  and  so  on,  like  tlie  branching  of  a 
great  tree  from  a  single  stem,  till  the  group  becomes  large. 

On  Extinction. 

We  have  as  yet  spoken  only  incidentally  of  the  disappear- 
ance of  species  and  of  groups  of  species.  On  the  theory  of 
natural  selection  the  extinction  of  old  forms  and  the  produc- 
tion of  ne\v  and  improved  forms  are  intimately  connected  to- 
gether. The  old  notion  of  all  tlie  inhabitants  of  the  earth  hav- 
ing been  swept  away  by  catastrophes  at  successive  periods  is 
very  generally  given  up,  even  by  tliose  geologists,  as  Elie  de 
Beaumont,  ]\Iurcliison,  Barrande,  etc.,  whose  general  views 
■would  naturally  lead  them  to  this  conclusion.  On  the  contrary, 
we  have  every  reason  to  believe,  from  the  study  of  the  tertiary 
formations,  that  species  and  groups  of  species  gradually  disap- 
pear, one  after  another,  first  from  one  sj^t,  then  from  another, 
and  finally  from  tlie  world.  In  some  few  cases,  however,  as  by 
the  breaking  of  an  isthmus  and  the  conseciuent  irrujition  of  a 
multitude  of  new  inhabitants  into  an  adjoining  sea,  or  by  the 
final  subsidence  of  an  island,  the  process  of  extinction  may  have 
been  rapid.  Both  single  species  and  whole  groups  of  species 
last  for  very  unequal  periods ;  some  groups,  as  we  have  seen, 
have  endured  from  the  earliest  known  dawn  of  life  to  the  pres- 
ent day ;  some  have  disappeared  before  the  close  of  the  paleo- 
zoic period.  No  fixed  law  seems  to  determine  the  length  of 
time  during  which  any  single  species  or  any  single  genus  en- 
dures. There  is  reason  to  believe  that  tlic  extinction  of  a 
whole  group  of  species  is  generally  a  slower  process  than  their 
production :  if  their  appearance  and  disappearance  be  repre- 
sented, as  before,  by  a  vertical  line  of  varying  tliickness,  tlie 
line  is  found  to  taper  more  gradually  at  its  ujiper  end,  wliich 
marks  tlie  progress  of  extermination,  than  at  its  lower  end, 
which  marks  the  first  appearance  and  the  early  increase  in 
number  of  the  species.  In  some  cases,  however,  the  extermina- 
tion of  whole  groups,  as  of  ammonites  toward  the  close  of  the 
secondary  periofl,  has  been  wonderfully  sudden. 

The  extinction  of  species  has  been  involved  in  the  most 
gratuitous  mystery.  Some  authors  have  even  supposed  that, 
as  the  individual  has  a  definite  length  of  life,  so  liav<;  species 
a  definite  duration.  No  one  can  have  marvelled  more  than  I 
have  done  at  the  extinction  of  species.  "When  I  found  in  La 
Plata  the  tooth  of  a  horse  embedded  witli  the  remains  of  Mas- 


300  EXTINCTION,  Chap.  X. 

iodon,  Mcgaihcrium,  Toxodon,  and  other  extinct  monsters, 
^vllich  all  coexisted  with  still  liviiii?  sliells  at  a  very  late  geolo- 
gical period,  I  Avas  filled  Avilh  astonishment;  for,  seeing  that 
the  horse,  since  its  introduction  by  the  Spaniards  into  South 
America,  has  run  wild  over  the  Avholc  country,  and  has  in- 
creased in  numbers  at  an  unparalleled  rate,  I  asked  myself 
what  could  so  recently  have  exterminated  the  former  horse  un- 
der conditions  of  life  apparently  so  favorable.  But  my  aston- 
ishment was  groundless.  Prof.  Owea  soon  perceived  that  the 
tooth,  though  so  like  that  of  the  existing  horse,  belonged  to 
an  extinct  species.  Had  this  horse  been  still  living,  but  in 
some  degree  rare,  no  naturalist  Avould  have  felt  the  least  sur- 
prise at  its  rarity ;  for  rarity  is  the  attribute  of  a  vast  number 
of  species  of  all  classes,  in  all  countries.  If  we  ask  ourselves 
why  this  or  that  species  is  rare,  we  answer  that  something  is 
unfavorable  in  its  conditions  of  life ;  but  what  that  something 
is,  we  can  hardly  ever  tell.  On  the  supposition  of  the  fossil- 
horse  still  existing  as  a  rare  species,  we  might  have  felt  certain, 
from  the  analogy  of  all  other  mammals,  even  of  the  slow-breed- 
ing ele])hant,  and  from  the  history  of  the  naturalization  of  the 
domestic  horse  in  South  Amei'ica,  that,  xuider  more  favorable 
conditions,  it  would,  in  a  very  few  years,  have  stocked  the 
whole  continent.  13ut  wc  could  not  have  told  what  the  un- 
favorable conditions  Avere  which  checked  its  increase,  Avhether 
some  one  or  several  contingencies,  and  at  what  period  of  the 
horse'^s  life,  and  in  what  degree,  they  severally  acted.  If  the 
conditions  had  gone  on,  however  slowly,  becoming  less  and 
less  favorable,  we  assuredly  should  not  have  perceived  the  fact, 
yet  the  fossil-horse  w^ould  certainly  have  become  rarer  and 
rarer,  and  finally  extinct — its  place  being  seized  on  by  some 
more  successful  competitor. 

It  is  most  diilicult  alwa3's  to  renaembcr  that  the  increase 
of  every  creature  is  constantly  being  checked  by  imperceived 
hostile  agencies  ;  and  that  these  same  unperceived  agencies 
are  amply  sufficient  to  cause  rarity,  and  finally  extinction.  So 
little  is  this  subject  understood,  that  I  have  heard  surprise  re- 
peatedly expressed  at  such  great  monsters  as  the  Mastodon 
and  the  more  ancient  Dinosaurians  having  become  extinct;  as 
if  mere  bodily  strength  ga\e  victory  in  the  battle  of  life.  Mere 
size,  on  the  contrary,  would  in  some  cases  determine,  as  has 
been  remarked  by  Owen, quicker  extermination  from  the  greater 
amount  of  requisite  food.  Before  man  inhabited  India  or  Africa, 
some  cause  must  have  checked  the  continued  increase  of  the 


CiiAP.  X.  EXTINCTION.  301 

existing;  elephant.  A  lii;;lily-capablc  judge,  Dr.  Falconer,  be- 
lieves that  it  is  chielly  insects  which,  from  incessantly  harass- 
ing and  weakening  the  elephant  in  India,  check  its  increase ; 
and  this  was  Bruce's  conclusion  with  respect  to  the  African 
elephant  in  Abj'ssinia.  It  is  certain  that  insects  and  blood- 
sucking bats  determine  the  existence  of  the  larger  naturalizec 
quadrupeds  in  several  parts  of  South  America. 

We  sec  in  many  cases  in  the  more  recent  tertiary  forma- 
tions, that  rarity  precedes  extinction ;  and  we  know  that  this 
has  been  the  progress  of  events  with  those  animals  which  have 
been  exterminated,  eillier  locally  or  wholly,  through  man's 
agency.  I  may  repeat  what  I  published  in  1815,  uamel}',  that 
to  admit  that  sjiecies  generally  become  rare  before  they  be- 
come extinct — to  feel  no  surprise  at  the  rarity  of  a  species, 
and  yet  to  marvel  greatly  when  the  species  ceases  to  exist,  is 
much  the  same  as  to  admit  that  sickness  in  the  individual  is 
t)ie  forerunner  of  death — to  feel  no  surprise  at  sickness,  but, 
when  the  sick  man  dies,  to  wonder  and  to  suspect  that  he  died 
by  some  deed  of  violence. 

The  theory  of  natural  selection  is  grounded  on  the  belief 
that  each  new  variety,  and  ultimately  each  new  species,  is  pro- 
duced and  maintained  by  having  some  advantage  over  those 
with  which  it  comes  into  competition ;  and  the  consequent 
oxtinctioii  of  the  less-favored  forms  almost  inevitably  follows. 
It  is  the  same  with  our  domestic  productions ;  when  a  new 
and  slightly-improved  variety  has  been  raised,  it  at  first  sup- 
plants the  less  improved  varieties  in  the  same  neighborhood; 
Avhen  much  improved,  it  is  transported  far  and  near,  like  our 
short-horn  cattle,  and  takes  the  place  of  other  breeds  in  other 
countries.  Thus  the  a})pcarance  of  new  forms,  and  the  disap- 
pearance of  old  forms,  both  those  naturally  and  those  artifi- 
cially produced,  are  bound  together.  In  nourishing  groups, 
the  number  of  new  specific  f(jrms  which  have  been  produced 
within  a  given  time,  has  at  some  periods  probably  been  greater 
than  the  number  of  the  old  specific  forms  which  have  been  ex- 
terminated; but  we  know  tliat  species  have  not  gone  on  indefi- 
nitely increasing,  at  least  during  the  later  geological  epochs ; 
so  that,  looking  to  later  times,  we  may  believe  that  the  pro- 
duction of  new  forms  has  caused  the  extinction  of  about  the 
same  number  of  old  forms. 

llie  competition  will  generally  be  most  severe,  as  formerly 
explained  and  illustrated  by  examples,  between  the  forms 
which  are  most  like  each  other  in   all  respects.     Hence   the 


302  EXTINCTION.  Chap.  X. 

improved  and  modified  dcsrcudants  of  a  species  will  generally 
cause  the  externiiiiatiou  of  the  parent-species;  and  if  many  new 
forms  have  been  developed  from  any  one  species,  the  nearest 
allies  of  that  species — i.  e.,  the  species  of  the  same  genus — will 
he  the  most  liable  to  extermination.  Thus,  as  I  believe,  a 
number  of  new  speci(3s  descended  from  one  species,  that  is,  a 
new  genus,  comes  to  sujiplant  an  old  geiuis,  belonging  to  the 
same  family.  But  it  must  often  have  happened  that  a  new 
species  belonging  to  some  one  group  has  seized  on  the  placfa 
occupied  by  a  species  belonging  to  a  distinct  group,  and  thus 
have  caused  its  extermination.  If  many  allied  forms  be  de- 
veloped from  the  successful  intruder,  many  will  have  to  yield 
tlunr  places ;  and  it  Avill  generally  be  the  allied  forms  which 
will  suffer  from  some  inherited  inferiority  in  common.  But 
whetlicr  it  be  species  belonging  to  the  same  or  to  a  distinct 
class,  which  have  yielded  their  places  to  other  modified  and 
improved  species,  a  few  of  the  sufferers  may  often  be  preserved 
for  a  long  time,  from  being  fitted  to  some  peculiar  line  of  life, 
or  from  inhabiting  some  distant  and  isolated  station,  where 
they  will  have  escaped  severe  competition.  For  instance, 
some  species  of  Trigonia,  a  great  genus  of  shells  in  the  second- 
ary formations,  survive  in  the  Australian  seas;  and  a  few  mem- 
bers of  the  great  and  almost  extinct  group  of  Ganoid  fishes 
still  inhabit  our  fresh  waters.  Therefore  the  utter  extinction 
of  a  group  is  generalh',  as  Ave  have  seen,  a  slower  process  than 
its  production. 

With  res^DCct  to  the  apparently  svidden  extermination  of 
whole  families  or  orders,  as  of  Trilobites  at  the  close  of  the 
paleozoic  period  and  of  Ammonites  at  the  secondary  period, 
we  must  remember  what  has  been  already  said  on  the  probable 
wide  intervals  of  time  between  our  consecutive  formations ; 
and  in  these  intervals  there  may  have  been  much  slow  exter- 
mination. I\Ioreover,  when,  by  sudden  immigration  or  by  un- 
usually rapid  development,  many  species  of  a  new  group  have 
taken  possession  of  an  area,  many  of  the  older  species  will  have 
been  exterminated  in  a  correspondingly  rapid  manner;  and  the 
fonns  Avhich  thus  yi(^^ld  their  places  vrill  commonly  be  allied, 
for  they  Avill  partake  of  the  same  inferiority  in  common. 

Thus,  as  it  seems  to  me,  the  manner  in  which  single  species 
and  Avliole  groups  of  species  become  extinct  accords  well  with 
the  theory  of  natural  selection.  We  need  not  marvel  at  ex- 
tinction ;  if  we  must  marvel,  let  it  be  at  our  own  presumption 
in  imagining  for  a  moment  tliat  wc  understand  the  many  com- 


CiiAr.  X.  FOKMS  OF  LIFE  CHANGING.  3O3 

plex  cuntinoencies,  on  which  ilic  existence  of  e;ich  species  de- 
pends. If  "SVC  for<ret,  for  an  instant,  that  each  species  tends  to 
-Ticreasc  inordinately,  and  that  some  check  is  always  in  action, 
yet  seldom  perceived  l)y  us,  the  whole  economy  of  Nature  will 
be  utterly  obscured.  Whenever  we  can  precisely  say  why  this 
species  is  more  alnmdant  in  individuals  than  that ;  why  this 
species  and  not  another  can  be  naturalized  in  a  given  country; 
then,  and  not  until  then,  we  may  justly  feel  surprised  why  we 
cannot  account  for  the  extinction  of  any  j)articular  species  or 
any  grouj)  of  species. 

On  the  Forms  of  Life  changlnff  almost  simultaneously 
throughout  the  World. 

Scarcely  any  jialeontological  discovery  is  more  striking 
than  the  fact  that  the  forms  of  life  change  almost  simultane- 
ously throughout  the  world.  Thus  our  European  Chalk  for- 
jnation  can  be  recognized  in  many  distant  parts  of  the  world, 
imder  the  most  different  climates,  where  not  a  fragment  of  the 
mineral  chalk  itself  can  be  found ;  namely,  in  North  America, 
in  equatorial  South  America,  in  Tierra  del  Fuego,  at  the  Cape 
of  Good  Hope,  and  in  the  peninsula  of  India.  For,  at  these 
distant  points,  the  organic  remains  in  certain  beds  present  an 
unmistakable  resemblance  to  those  of  the  Chalk.  It  is  not  that 
the  same  species  are  met  with  ;  for  in  some  cases  not  one 
species  is  identically  the  same,  but  they  belong  to  the  same 
families,  genera,  and  sections  of  genera,  and  sometimes  arc 
Kimilarly  characterized  in  such  trilling  points  as  mere  superficial 
sculpture.  Moreover,  other  forms,  which  are  not  found  in  the 
Chalk  of  Europe,  but  which  occur  in  the  formations  either  above 
or  below,  occur  in  the  same  order  at  these  distant  points  of  the 
world.  In  the  several  successive  paleozoic  formations  of  Rus- 
sia, Western  Europe,  and  North  America,  a  similar  parallelism 
in  the  forms  of  life  has  been  observed  by  several  authors  :  so  it 
is,  according  to  Lycll,  with  the  several  European  and  North 
American  tertiary  deposits.  Even  if  the  few  fossil  species 
which  are  common  to  the  Old  and  New  Worlds  were  kept 
wholly  out  of  view,  the  general  ])arallelism  in  the  successive 
forms  of  life,  in  the  paleozoic  and  tertiary  stages,  would  still 
be  manifest,  and  the  several  formations  could  be  easily  corre- 
lated. 

These  observations,  however,  relate  to  the  marine  inhabit- 
ants of  the  Avorld:  we  have  not  sufTirient  data  to  judge  whelhcr 


304  FORMS   OF  LIFE  CHANGING  Ciiai-.  X. 

the  productions  of  llie  land  and  of  fresh  water  at  distant  points 
clianfj^e  in  the  same  jiarallcl  manner.  We  may  doubt  wliethcr 
thoy  have  tluis  changed:  if  the  Meg-atherium,  Milodon,  Macra- 
iiclicnia,  and  Toxodon  had  been  brought  to  Europe  from  La 
Plata,  without  any  information  in  regard  to  their  geological 
position,  no  one  would  have  suspected  that  they  had  coexisted 
with  sea-shells  all  still  living;  but  as  these  anomalous  monsters 
coexisted  with  the  Mastodon  and  Horse,  it  might  at  least  have 
been  inferred  that  they  had  lived  during  one  of  the  later  ter- 
tiary stages. 

When  the  marine  forms  of  life  are  spoken  of  as  haWng 
changed  simultaneously  throughout  the  world,  it  must  not  be 
supposed  that  tliis  expression  relates  to  the  same  thousandth 
or  ten-thousandth  year,  or  even  that  it  has  a  very  strict  geologi- 
cal sense  ;  for  if  all  the  marine  animals  now  living  in  Europe, 
and  all  those  that  lived  in  Europe  during  the  pleistocene  period 
(a  very  remote  period  as  measured  by  years,  including  the 
Avhole  glacial  epoch)  Avcre  compared  Avith  those  now  existing 
in  South  America  or  in  Australia,  the  most  skilful  naturalist 
would  hardly  be  able  to  say  whetlicr  the  present  or  the  pleis- 
tocene inhabitants  of  Europe  resembled  most  closely  those  of 
the  southern  hemisphere.  So,  again,  several  highly-competent 
obs(>rvers  maintain  that  the  existing  productions  of  the  United 
States  are  more  closely  related  to  those  which  lived  in  Europe 
during  certain  late  tertiary  stages,  than  to  the  present  inhabit- 
ants of  Europe ;  and  if  this  be  so,  it  is  e\ddent  that  fossilifer- 
ous  beds  now  being  deposited  on  the  shores  of  North  America 
would  hereafter  be  liable  to  be  classed  with  somewhat  older 
European  beds.  Nevertheless,  looking  to  a  remotely  future 
epoch,  there  can  be  little  doubt  that  all  the  more  modern  ma- 
rine formations,  namely,  the  upper  pliocene,  the  pleistocene 
and  strictly  modern  beds,  of  Europe,  North  and  South  Amer- 
ica, and  Australia,  from  containing  fossil  remains  in  some  de- 
gree allied,  and  from  not  including  those  forms  which  are  found 
only  in  the  older  underlying  deposits,  would  be  correctly 
ranked  as  simultaneous  in  a  geological  sense. 

The  fact  of  the  forms  of  life  changing  simultaneously,  in  the 
above  large  sense,  at  distant  parts  of  the  Avorld,  has  greatly 
struck  those  admirable  observers,  MM.  do  Verneuil  and  d'Arcli- 
iac.  After  referring  to  the  parallelism  of  the  paleozoic  forms 
of  life  in  various  pails  of  Europe,  they 'add  :  "  If.  struck  by  tliis 
strange  sequence,  Ave  turn  our  attention  to  North  AmcricM, 
and  there  discover  a  series  of  analogous  iihenomena,  it  wi!.' 


CiiAP.  X.  THROUGHOUT  THE  WORLD  305 

appear  certain  that  all  these  modifications  of  species,  tlieir  ex- 
tinction, and  the  introduction  of  new  ones,  cannot  be  owin^r  to 
move  chani^es  in  marine  currents  or  other  causes  more  or  less 
local  and  temporarv,  but  de])cnd  on  general  laws  which  govern 
the  whole  animal  kingdom."  M.  Barrande  has  made  forcible 
remarks  to  j)recisely  tin;  same  eflect.  It  is,  indeed,  quite  futile 
to  look  to  changes  of  currents,  climate,  or  other  physical  con- 
ditions, as  the  cause  of  these  great  mutations  in  the  forms  of 
lift;  throughout  the  world,  under  the  most  different  climates. 
Wc  must,  as  Barrande  has  remarked,  look  to  some  special  law. 
AVe  shall  see  this  more  clearly  when  Ave  treat  of  the  present 
distribution  of  organic  l)cings,  and  find  how  slight  is  the  rela- 
tion between  the  ])hysical  conditions  of  various  countries,  and 
the  nature  of  their  inhabitants. 

This  great  fact  of  the  parallel  succession  of  the  forms  of  life 
througlu^ut  the  world,  is  explicable  on  the  theory  of  natural 
selection.  New  species  arc  formed  by  having  some  advantage 
over  older  forms ;  and  the  forms,  whicli  are  already  dominant, 
or  have  some  advantage  over  the  other  forms  in  their  own 
country,  would  be  the  most  likely  to  give  birth  to  the  greatest 
number  of  new  varieties  or  incipient  sjiccies.  We  have  distinct 
evidence  on  this  head,  in  the  plants  which  are  dominant,  that 
is,  which  are  commonest  and  most  widely  diffused,  producing 
the  greatest  numljcr  of  new  varieties.  It  is  also  natural  that 
the  dominant,  varying,  and  far-spreading  species,  which  already 
'lave  invaded  to  a  certain  extent  the  territories  of  other  species, 
should  be  those  which  would  have  the  best  chance  of  spreading 
still  further,  and  of  giving  rise  in  new  countries  to  other  new 
varieties  and  species.  The  process  of  diffusion  would  often  be 
very  slow,  depending  on  climatal  and  geographical  changes, 
on  strange  accidents,  and  on  the  gradual  acclimatization  of  new 
species  to  the  various  climates  through  which  they  might  have 
to  jxiss,  but  in  the  course  of  time  the  dominant  forms  would 
generally  succeed  in  spreading,  and  would  ultimately  prevail. 
Th('  diffusion  would,  it  is  probable,  be  slower  with  the  terres- 
trial inhabitants  of  distinct  continents  than  with  the  marine 
inhabitants  of  llie  continuous  sea.  We  might  therefore  expect 
to  find,  as  we  do  find,  a  less  strict  degree  of  parallelism  in  the 
succession  of  the  productions  of  the  land  than  with  those  of  the 
sea. 

Thus,  as  it  seems  to  me,  the  parallel,  and,- taken  in  a  large 
sense,  simultaneous,  succession  of  the  same  forms  of  life  through- 
out the  world,  accords  well  witli  tlic  j>rinciple  of  new  species 


306  FORMS   OF  LIFE  CHANGING  Chap.  X. 

havinfi^  been  formed  by  dominant  species  spreading  widely  and 
varying;  the  new  species  thus  produced  being  themselves  dom- 
inant, owing  to  their  having  had  some  advantage  over  their 
already  dominant  parents,  as  well  as  over  other  species,  ana 
again  spreading,  varying,  and  producing  new  forms.  The  old 
forms  which  are  beaten  and  Avhicli  yield  their  places  to  the  new 
and  victorious  forms,  will  generally  be  allied  in  groups,  from 
inheriting  some  inferiority  in  common ;  and  therefore,  as  new 
and  imjjroved  groups  spread  throughout  the  world,  old  groups 
disappear  from  the  world ;  and  the  succession  of  forms  every- 
where tends  to  corres])ond  both  in  their  first  appearance  and 
final  disappearance. 

There  is  one  other  remark  connected  with  this  subject  worth 
making.  I  have  given  my  reasons  for  believing  that  most  of 
our  great  formations,  rich  in  fossils,  were  deposited  during 
periods  of  subsidence ;  and  that  blank  intervals  of  vast  dura- 
tion, as  far  as  fossils  are  concerned,  occurred  during  the  periods 
when  the  bed  of  the  sea  was  cither  stationary  or  rising,  and 
likewise  when  sediment  was  not  thrown  down  quiclcly  enough 
to  embed  and  preserve  organic  remains.  During  these  long 
and  blank  intervals  I  suppose  that  the  inhabitants  of  each  re- 
gion underwent  a  considerable  amount  of  modification  and  ex- 
tinction, and  that  there  was  much  migration  from  other  parts 
of  the  world.  As  we  have  reason  to  believe  that  large  areas 
are  affected  by  the  same  movement,  it  is  probable  that  strictly 
contemporaneous  formations  have  often  been  accumulated  over 
very  wide  spaces  in  the  same  quarter  of  the  world ;  but  we  are 
very  far  from  having  any  right  to  conclude  that  this  has  invari- 
ably been  the  ease,  and  that  large  areas  have  invariably  been 
affected  by  the  same  movements.  Wlien  two  formations  have 
been  deposited  in  two  regions  during  nearly,  but  not  exactly, 
the  same  period,  we  should  find  in  both,  from  the  causes  ex- 
plained in  the  foregoing  paragraphs,  the  same  general  succes- 
sion in  the  forms  of  life ;  but  the  species  would  not  exactly 
correspond ;  for  there  will  have  been  a  little  jnore  time  in  the 
one  region  than  in  the  other  for  modification,  extinction,  and 
immigration. 

I  suspect  that  cases  of  this  nature  occur  in  Europe.  Mr. 
Prestwich,  in  his  admirable  memoirs  on  the  eocene  dejiosits  of 
England  and  France,  is  able  to  draw  a  close  general  parallelism 
between  the  successive  stages  in  the  two  countries ;  but  when 
he  compares  certain  stages  in  England  with  those  in  France, 
although  he  finds  in  both  a  curious  accordance  in  the  numbers 


Chap.  X.  TIIIIOUGIIOUT  THE   WOULD.  ,^07 

of  tlie  species  bclongiiijr  to  the  same  genera,  yet  the  species 
thetiisehes  diircr  in  a  manner  very  difTicult  to  account  for,  con- 
sidcrin<x  the  proximit}-  of  tlic  tuo  areas,  unless  indeed  it  be 
assumed  that  an  isthmus  separated  two  seas  inhabited  by  dis- 
tinct but  contemporaneous  faunas.  Lyell  has  made  similar 
observations  on  some  of  the  later  tertiary  formations.  Barrande, 
also,  shows  that  there  is  a  striking  general  parallelism  in  the 
successive  Silurian  deposits  of  Bohemia  and  Scandinavia ;  never- 
theless he  finds  a  surprising  amount  of  dillcrence  in  the  species. 
If  the  several  formations  in  these  regions  have  not  been  de- 
jiosited  during  the  same  exact  periods — a  formation  in  one  re- 
gion often  corresponding  with  a  blank  interval  in  the  other — 
and  if  in  both  regions  the  species  have  gone  on  slowly  chan- 
ging during  tlie  accumulation  of  tlie  several  formations,  and 
(hning  the  long  intervals  of  time  between  tliem ;  in  this  case 
the  several  formations  in  the  two  regions  could  be  arranged  in 
the  same  order,  in  accordance  with  the  general  succession  of 
the  forms  of  life,  and  the  order  would  falsely  appear  to  be  strictly 
parallel ;  nevertheless  the  species  would  not  be  all  the  same  in 
the  aiiparcntly  corresponding  stages  in  the  two  regions. 

On  the  Affinities  of  J^xtinct  Species  to  each  other,  and  to 
Livinf/  J/ornis. 

Let  us  now  look  to  the  mutual  affinities  of  extinct  and  liv- 
ing species.  They  all  fall  into  a  few  grand  classes  ;  and  this 
fact  is  at  once  explain(Ml  on  the  princij)le  of  descent.  The  more 
ancient  any  form  is,  the  more,  as  a  general  rule,  it  differs  from 
living  forms.  But,  as  Buckland  long  ago  remarked,  all  extinct 
species  can  be  classed  eitlier  in  still  existing  grou})s,  or  between 
tliem.  That  the  extinct  forms  of  life  help  to  fill  up  the  inter- 
vals between  existing  genera,  families,  and  orders,  cannot  be 
disputed.  For  if  we  confine  our  attention  cither  to  the  living 
or  to  the  extinct  alone,  the  series  is  far  less  perfect  than  if  we 
combine  both  into  one  general  system.  With  respect  to  the 
vertebrata,  whole  pages  could  be  filled  with  illustrations  from 
Owen,  showing  how  extinct  animals  fall  in  between  existing 
groups.  Cuvier  ranked  the  Ruminants  and  Pachyderms,  as  the 
two  most  distinct  orders  of  mammals  ;  but  Owen  has  discovered 
so  many  fossil  links,  that  he  has  had  to  alter  th(;  whole  classifi- 
cation, and  has  placed  certain  j)achyderms  in  the  same  sub-order 
with  nnuinants :  for  example,  he  dissolves  by  fine  gradations 
the  apparently  wide  difference  between  the  pig  and  the  camel. 


SOS  AFFINITIES  OF  EXTINCT  SPECIES.  Cii.vp.  X. 

Another  distinguished  paleontologist,  M.  Gaudry,  shows,  in 
the  most  striking  manner,  that  very  many  of  the  fossil  mam- 
mals discDvered  by  him  in  Attica,  connect  in  the  plainest  man- 
ner existing  genera.  AMiat  a  -wonderful  intermediate  form  is 
the  Tyiiotherium  from  South  America,  as  the  name  given  to  it 
by  Prof.  Gervais  expresses,  and  Avliich  cannot  be  placed  in  any 
existing  order  of  mammals  !  Even  the  wide  interval  between 
lairds  and  reptiles  has  been  shown  by  Prof.  Huxley  to  be  par- 
tially bridged  over  in  the  most  unexpected  manner,  by,  on  the 
one  hand,  the  ostrich  and  extinct  Archeopteryx ;  and,  on  the 
other  hand,  the  Compsognathus,  one  of  the  Dinosaurians — that 
group  which  includes  the  most  gigantic  of  all  terrestrial  rep- 
tiles. Turning  to  the  Invertebrata,  Barrande  asserts,  and  a 
higher  authority  could  not  be  named,  that  he  is  every  day 
taught  that,  although  paleozoic  animals  can  certainly  be  classed 
under  existing  groups,  yet  that  at  this  ancient  period  the 
groups  were  not  so  distinctly  separated  from  each  other  as  they 
now  are. 

Some  writers  have  objected  to  an}'  extinct  species  or  group 
of  species  being  considered  as  intermediate  between  living 
species  or  groups.  If  by  this  term  it  is  meant  that  an  extinct 
form  is  directly  intermediate  in  all  its  characters  between  two 
living  forms,  the  objection  is  valid.  But  in  a  natural  classifi- 
cation many  fossil  species  certainly  stand  between  living  spe- 
cies, and  some  extinct  genera  between  living  genera,  even 
between  genera  belonging  to  distinct  families.  The  most 
common  case,  especially  with  respect  to  very  distinct  groups, 
such  as  fish  and  reptiles,  seems  to  be,  that,  supposing  them  to 
be  distinguished  at  the  present  day  by  a  dozen  characters,  the 
ancient  members  are  separated  by  a  somewhat  lesser  number 
of  characters,  so  that  the  two  groups,  though  formerly  quite 
distinct,  made  at  that  period  a  somewhat  nearer  approach  to 
each  other. 

It  is  a  common  belief  that  the  more  ancient  a  form  is,  by 
so  much  the  more  it  tends  to  connect  by  some  of  its  characters 
groups  now  widely  separated  from  each  other.  This  remark 
no  doubt  must  be  restricted  to  those  groups  Avhich  have  mider- 
gone  much  change  in  the  course  of  geological  ages ;  and  it 
would  be  difficult  to  prove  the  truth  of  the  proposition,  for 
every  now  and  then  even  a  living  animal,  as  the  Lepidosiren, 
is  discovered  having  affinities  directed  toward  very  distinct 
groups.  Yet  if  we  compare  the  older  Reptiles  and  Batra- 
chians,  the  older  Fish,  the  older  Cephalopods,  and  the  eocene 


Chap.  X.  AFFINITIES  OF  EXTINCT  SPECIES.  309 

Mammals,  witli  llio  more  recent  members  of  the  same  classes, 
we  must  admit  that  there  is  truth  in  tlie  i-emark. 

Let  us  see  how  far  these  several  facts  and  inferences  accord 
with  tlic  theory  of  descent  with  modification.  As  the  subject 
is  somewhat  complex,  I  must  request  the  reader  to  turn  to  the 
diafi^ram  in  the  fourth  chapter.  We  may  suppose  that  the 
numbered  letters  represent  genera,  and  the  dotted  lines  di- 
verging from  them  the  species  in  each  genus.  The  diagram 
is  much  too  simple,  too  few  genera  and  too  few  species  being 
given,  but  this  is  unimportant  for  us.  The  horizontal  lines 
may  represent  successive  geological  formations,  and  all  the 
forms  beneath  the  uppermost  line  may  be  considered  as  ex- 
tinct. The  three  existing  genera,  «'*,  Q^*,])'*,  will  form  a  small 
family ;  i'*  and  _/"'*,  a  closely-allied  family  or  sub-family ;  and 
o'*,  e'*,  Wi",  a  third  lamily.  These  three  families,  together  vvitli 
the  many  extinct  genera  on  the  several  lines  of  descent  di- 
verging irom  the  parent-form  (A),  will  form  an  order;  for  all 
Avill  have  inherited  something  in  common  from  their  ancient 
and  common  ])rogenitor.  On  the  principle  of  the  continued 
tendency  to  divergence  of  character,  which  was  formerly  illus- 
trated by  this  diagram,  the  more  recent  any  form  is,  the  more 
it  will  generally  differ  from  its  ancient  progenitor.  Hence  we 
can  understand  the  rule  that  the  most  ancient  fossils  ditfer  most 
from  existing  forms.  We  must  not,  hoAvever,  assume  that  di- 
vergence of  character  is  a  necessary  contingency;  it  depends 
solely  on  the  descendants  from  a  species  being  thus  enabled 
to  seize  on  many  and  different  places  in  the  economy  of  Natme. 
Therefore  it  is  quite  possible,  as  we  have  seen  in  the  case  of 
some  Silurian  forms,  that  a  species  might  go  on  being  slightly 
modified  in  relation  to  its  slightly-altered  conditions  of  life, 
and  yet  retain  throughout  a  vast  period  the  same  general 
characteristics.  This  is  represented  in  the  diagram  by  the  let- 
ter f'\ 

All  the  many  forms,  extinct  and  recent,  descended  from 
(A),  mak(%  as  Ix-fore  remarked,  one  order;' and  this  order,  from 
the  continued  eflects  of  extinction  and  divergence  of  character, 
has  l)ecoine  divided  into  several  sul>families  and  families,  some 
of  which  are  supposed  to  have  perished  at  dilVercnt  periods, 
and  some  to  have  endured  to  the  present  da}'. 

By  looking  at  the  diagram  we  can  sec  that  if  many  of  the 
extinct  forms,  supposed  to  be  embedded  in  the  successive  for- 
mations, were  discovered  at  several  jioints  low  down  in  the 
series,  the  three  existing  families  on  the  uppermost  line  would 


310  AFFINITIES   OF  EXTINX'T  SrFX'IKS.  Chap.  X. 

be  rendered  less  distinct  from  each  otlior.  If,  for  instance,  the 
g'enera  «',  «V  ^'"5  /*»  ''^*»  ^''^S  ''^'^  Averc  disinterred,  these  three 
families  would  be  so  closely  linked  together  that  they  proba- 
bly M'ould  have  to  be  xniited  into  one  great  family,  in  nearly 
the  same  manner  as  has  occurred  -with  ruminants  and  certain 
pach^'dtM-ms.  Yet  he  who  objected  to  call  the  extinct  genera 
which  thus  linked  the  living  genera  of  three  families  together, 
intermediate  in  character,  would  be  justified,  as  they  are  inter- 
mediate, not  directly,  but  only  by  a  long  and  circuitous  course 
through  many  "vndely-different  forms.  If  many  extinct  forms 
were  to  be  discovered  above  one  of  the  middle  horizontal  lines 
or  geological  formations — for  instance,  above  No.  VI. — but 
none  from  beneatli  this  line,  then  only  two  of  the  families 
(those  on  the  left  hand,  «'*,  etc.,  and  b^*,  etc.)  would  have  to  be 
imited  into  one ;  and  there  wovild  remain  two  families,  which 
would  be  less  distinct  from  each  other  than  they  were  before 
the  discovery  of  the  fossils.  So,  again,  if  the  three  families 
formed  of  eight  genera  («"  to  ni^*),  on  the  uppermost  line, 
be  supposed  to  differ  from  each  other  by  half  a  dozen  impor- 
tant characters,  then  the  families  which  existed  at  the  peiiod 
marked  VI.  would  certainly  have  differed  from  each  other  by 
a  less  numljer  of  characters ;  for  they  would  at  this  early  stage 
of  descent  have  diverged  in  a  less  degree  from  their  common 
progenitor.  Thus  it  comes  that  ancient  and  extinct  genera 
are  often  in  some  slight  degree  intermediate  in  character  be- 
tween their  modilled  descendants,  or  between  their  collateral 
relations. 

In  Nature  the  case  will  be  far  more  complicates!  than  is 
represented  in  the  diagram ;  for  the  groups  "will  have  been 
more  numerous,  they  will  have  endured  for  extremely  unequal 
lengths  of  time,  and  Avill  have  been  modified  in  various  degrees. 
As  we  possess  only  the  last  volume  of  the  geological  record, 
and  that  in  a  very  broken  condition,  Ave  have  no  right  to  expect, 
except  in  rare  cases,  to  fill  up  the  wide  intervals  in  the  natural 
system,  and  thus  imife  distinct  fiimilies  or  orders.  All  that  we 
have  a  right  to  expect  is,  that  those  groups  which  have  within 
knoA\ni  geological  periods  undergone  much  modification,  should 
in  the  older  formations  make  some  slight  approach  to  each 
other ;  so  that  the  older  members  should  differ  less  from  each 
other  in  some  of  their  characters  than  do  the  existing  members 
of  the  same  groups;  and  this,  by  the  concurrent  evidence  of 
our  best  paleontologists,  is  frequently  the  case. 

Thus,  on  the  thcorv  of  dcsrcnt  witli   modification,  the  main 


CujLT.X.  AFFINITIES  OF  EXTINCT  SPECIES.  31 1 

facts  with  respect  to  the  mutual  affinities  of  the  extinct  forms 
of  life  to  each  other  and  to  livinf^  forms,  are  explained  in  a 
satisfactory  manner.  And  they  are  wholly  inexplicable  on  any 
other  view. 

On  this  same  theory,  it  is  evident  that  the  fauna  of  any 
one  great  ])eriod  in  the  earth's  history  will  be  intermediate 
in  g'eneral  character  between  that  which  preceded  and  that 
which  succeeded  it.  Thus  the  species  which  lived  at  the  sixth 
p^reat  stage  of  descent  in  the  diagram  are  the  modified  ofTsjjring 
of  those  which  lived  at  the  fifth  stage,  and  are  the  parents  of 
1  hose  which  became  still  more  modified  at  the  seventh  stage; 
hence  they  could  hardly  fail  to  be  nearly  intermediate  in  char- 
acter between  the  forms  <jf  life  above  and  below.  We  must,  hoAV- 
ever,  allow  ior  the  entire  extinction  of  some  preceding  forms, 
and  in  any  one  region  for  the  immigration  of  new  fijrms  from 
other  regions,  and  for  a  large  amount  of  modification  during 
the  long  and  blank  intervals  between  the  successive  forma- 
tions. Subject  to  these  allowances,  the  fauna  of  each  geolo- 
gical period  undoubtedly  is  intermediate  in  character  between 
the  preceding  and  succeeding  faunas.  I  need  give  only  one 
instance,  namely,  the  manner  in  which  the  fossils  of  the  Devo- 
nian system,  when  this  system  was  first  discovered,  were  at 
once  recognized  by  paleontologists  as  intermediate  in  charac- 
ter between  those  of  the  overlying  carboniferous,  and  under- 
lying Silurian  system.  But  each  fauna  is  not  necessarily  ex- 
actly intermediate,  as  unequal  intervals  of  time  have  elapsed 
between  consecutive  formations. 

It  is  no  real  objection  to  the  truth  of  the  statement  that 
the  fauna  of  each  period  as  a  whole  is  nearly  intermediate  in 
character  between  the  preceding  and  succeeding  faunas,  that 
certain  genera  offer  exceptions  to  the  rule.  For  instance, 
mastodons  and  elephants,  when  arranged  by  Dr.  Falconer  in 
two  scries,  first  according  to  their  mutual  affinities  and  then 
according  to  their  periods  of  existence,  do  not  accord  in  ar- 
rangement. The  species  extreme  in  character  are  not  the  old- 
est or  the  most  recent ;  nor  are  those  which  are  intermediate 
in  character,  intermediate  in  age.  But  supposing  for  an 
instant,  in  this  and  other  sucli  cases,  "that  the  recoril  of  the 
lir^t  appearance  and  disappearance  of  the  species  was  perfect, 
we  have  no  reason  to  believe  that  forms  successively  produced 
necessarily  endure  for  corresponding  lengths  of  time  :  a  very 
ancient  form  might  occasionally  last  much  longer  than  a  form 
elsewhere  subsequently  produced,  csjiecially   in   the  case  of 


312  AFFINITIES  OF  EXTINCT  SrECIES.  Chap.  X. 

ten-estrial  productions  inliabiting  separated  districts.  To  com- 
pare small  tliiii;^s  with  p^reat  :  if  the  principal  living  and  ex- 
tinct races  of  the  domestic  pigeon  were  arranged  as  well  as 
they  could  be  in  serial  affinity,  this  arrangement  would  not 
accord  closely  with  the  order  in  time  of  their  production,  and 
even  less  with  the  order  of  their  disappearance ;  for  the  par- 
cnt-rock-pigeon  still  lives  ;  and  many  varieties  between  the 
rock-pigeon  and  the  carrier  have  become  extinct ;  and  carriers 
Avhich  are  extreme  in  the  important  character  of  length  of 
beak  originated  earlier  than  short-beaked  tumblcrs,which  are 
at  the  opposite  end  of  the  series  in  this  respect. 

Closely  connected  with  tlie  statement  that  the  organic  re- 
mains from  an  intermediate  formation  are  in  some  degree  in- 
termediate in  character,  is  the  fact,  insisted  on  by  all  paleon- 
tologists, that  fossils  from  two  consecutive  formations  are  far 
more  closclj'  related  to  each  other  than  are  the  fossils  from 
two  remote  formations.  Pictet  gives  us  a  well-known  in- 
stance, the  general  resemblance  of  the  organic  remains  from 
the  several  stages  of  the  Chalk  formation,  though  the  species 
are  distinct  in  each  stage.  This  fact  alone,  from  its  generality, 
seems  to  have  shaken  Prof.  Pictet  in  his  firm  belief  in  the  im- 
mutability of  species.  He  who  is  acquainted  with  the  distribu- 
tion of  existing  species  over  the  globe,  will  not  attempt  to 
account  for  the  close  resemblance  of  distinct  species  in  close- 
ly consecutive  formations,  by  the  ph^-sical  conditions  of  the 
ancient  areas  having  remained  nearly  the  same.  Let  it  be  re- 
membered that  the  forms  of  life,  at  least  those  inhabiting  the 
sea,  have  changed  almost  simultaneously  throughout  the  Avorld, 
and  therefore  under  the  most  different  climates  and  conditions. 
Consider  the  prodigious  vicissitudes  of  climate  during  the  pleis- 
tocene period,  which  includes  the  whole  glacial  epoch,  and  note 
how  little  the  specific  forms  of  the  inhabitants  of  the  sea  have 
been  affected. 

On  the  theory  of  descent,  the  full  meaning  of  the  fossil  re- 
mains from  closely-consecutive  formations  being  closely  related, 
though  ranked  as  distinct  species,  is  obvious.  As  the  accumu- 
lation of  each  formation  has  often  been  interrupted,  and  as 
long  blank  intervals  have  intervened  between  successive  forma- 
tions, we  ought  not  to  expect  to  find,  as  I  attempted  to  show 
in  the  last  chapter,  in  any  one  or  in  any  two  formations  all  the 
intermediate  vaiietics  between  the  species  which  appeared  at 
the  commencement  and  close  of  these  periods  :  but  we  ought 
to  find  after   intervals,   very  long  as  measureil  by  years,  but 


CnAP.  X.  STATE  OF  DEVELOPMENT.  31 3 

only  moderately  lonp;'  as  measured  f^coloo-ically,  closely-allied 
Forms,  or,  as  they  have  been  called  by  some  authors,  represent- 
ative species ;  and  these  assuredly  we  do  find.  We  find,  in 
short,  such  evidence  of  the  slow  and  scarcely-sensible  muta- 
tion of  specific  forms  as  we  have  the  right  to  expect. 

On  the  State  of  DevelojJmoit  of  AncieJit  comjtared  with  Liv- 
ing Forms. 

We  have  seen  in  the  fourth  chapter  that  the  degree  of 
differentiation  and  specialization  of  the  parts  in  all  organic 
beings,  when  arrived  at  maturity,  is  the  best  standard,  as  yet 
suggested,  of  their  degree  of  perfection  or  highness.  We 
have  also  seen  that,  as  the  specialization  of  parts  and  organs 
is  an  advantage  to  each  being,  so  natural  selection  will  tend 
to  render  the  organization  of  each  being  more  specialized  and 
perfect,  and  in  this  sense  higher ;  not  but  that  it  may  and 
will  leave  many  creatures  with  siin])li'  and  unimproved  struct- 
ures fitted  for  simple  conditions  of  life,  and  in  some  cases  will 
even  degrade  or  simplify  the  organization,  yet  leaving  such 
degraded  beings  better  fitted  for  their  new  walks  of  life.  In 
another  and  more  general  manner,  new  species  will  become 
superior  to  their  predecessors;  for  they  will  have  to  beat  in  the 
struggle  for  life  all  the  older  forms  with  which  they  come  into 
close  competition.  We  may  therefore  conclude  that,  if  under 
n  nearly  similar  climate  the  eocene  inhabitants  of  the  world 
could  be  put  into  competition  with  the  existing  inhobitants, 
(he  former  would  be  beaten  and  exterminated  by  the  latter,  as 
would  the  secondary  by  the  eocene,  and  the  paleozoic  by  the 
secondary  forms.  So  that  by  this  fundamental  test  of  victory 
in  the  battle  for  life,  as  well  as  by  the  standard  of  the  spociali- 
zaticjn  of  organs,  modern  forms  ought  on  the  theory  of  natu- 
ral selection  to  stand  higher  than  ancient  fonns.  Is  this  the 
case  ?  A  large  majority  of  paleontologists  wcnikl  answer  in 
the  affirmative  ;  and  I  suppose  that  the  answer  must  he  ad- 
mitted as  true,  though  dillicult  of  full  proof. 

It  is  no  valid  objection  to  this  conclusion,  that  certain 
BrachiopcKls  have  been  but  slightly  modilied  from  an  extremely 
remote  geological  epoch.  It  is  not  an  insuperable  diniculty 
that  Foramiiiifera  have  not,  as  insisted  on  b}*  Dr.  ('arp<'nter, 
])rogress*ed  in  organization  since  even  the  Laurentian  epoch  : 
for  some  organisms  would  have  to  remain  iitted  for  simple  con- 
ditions of  life,  and  what  could  be  better  fitted  for  this  end  than 
14 


314  STATE   OF  DEVELOPMENT  OF  Chap.  X. 

these  lowly-organized  Protozoa  ?  It  is  no  great  difficulty  that 
fresh-water  shells,  as  Prof,  Piiillips  has  urged,  have  remained 
almost  unaltered  from  the  time  when  they  first  ajipeared  to 
the  present  day ;  for  these  shells  will  have  been  subjected  to 
less  severe  competition  than  the  moUusks  inhabiting  the  more 
extensive  area  of  the  sea  with  its  innumerable  inhabitants. 
Such  objections  as  the  above  v/ould  be  fatal  to  any  view  which 
included  advance  in  organization  as  a  necessary  contingent. 
They  would  likewise  be  fatal  to  my  view  if  Foraminifera,  for 
instance,  could  be  proved  to  have  first  come  into  existence, 
during  the  Laurentian  epoch,  or  Brachiopods  during  the  Cam- 
brian formation  ;  for,  in  this  case,  there  Avould  not  have  been 
time  sufficient  for  the  development  of  these  organisms  up  to 
the  standard  which  they  then  reached.  When  once  advanced 
up  to  any  given  point,  there  is  no  necessity  on  the  theory  of 
natvu'al  selection  for  their  further  continued  progress ;  though 
they  will,  during  each  successive  age,  have  to  be  slightly 
modified,  so  as  to  hold  their  places  in  relation  to  the  changing 
conditions  of  life.  All  such  objections  hinge  on  the  question 
whether  w^e  I'eally  know  how  old  the  world  is,  and  at  what 
periods  the  various  forms  of  life  first  appeared ;  and  this  may 
be  disputed. 

The  problem  whether  organization  on  the  whole  has  ad- 
vanced is  in  many  ways  excessively  intricate.  The  geological 
record,  at  all  times  imperfect,  does  not  extend  far  enough  back, 
as  I  believe,  to  show  Avith  unmistakable  clearness  that  within 
the  known  history  of  the  world  organization  has  largely  ad- 
vanced. Even  at  the  present  day,  looking  to  members  of  the 
same  class,  naturalists  are  not  unanimous  which  forms  are  to  be 
ranked  as  highest:  thus,  some  look  at  the  selaceans  or  sharks, 
from  their  approach  in  some  important  points  of  structure  to  rep- 
tiles, as  the  highest  fish  ;  others  look  at  the  teleosteans  as  the 
highest.  The  ganoids  stand  intermediate  between  the  selaceans 
and  teleosteans  ;  the  latter  at  the  present  day  are  largely  pre- 
ponderant in  number ;  but  formerly  selaceans  and  ganoids  alone 
existed  ;  and  in  this  case,  according  to  the  standard  of  highness 
chosen,  so  will  it  be  said  that  fishes  have  advanced  or  retro- 
graded in  organization.  To  attempt  to  compare  in  the  scale 
of  highness  members  of  distinct  types  seemed  hopeless  :  who 
will  decide  whether  a  cuttle-fish  be  higher  tlian  a  bee — that  in- 
sect which  the  great  Von  Baer  believed  to  be  "  in  fact  more 
highly  organized  than  a  fish,  although  upon  another  type?" 
In  the  comjilex  struggle  for  life  it  is  quite  credible  that  cms- 


Chap.  X.  ANCIENT  AND  LIVING  FORMS.  315 

taceaus,  not  very  high  in  tlrcir  own  class,  might  beat  cephalo- 
pods,  tlic  highest  nioUusks  ;  and  such  crustaceans,  though  not 
highlv  devek)pccl,  wouhl  stand  very  high  in  the  scale  of  inverte- 
brate animals  if  judged  by  the  most  decisive  of  all  trials — the 
law  of  battle.  Besides  these  inherent  difficulties  in  deciding 
which  forms  are  the  most  advanced  in  organization,  we  ouglit 
not  solely  to  compare  the  highest  members  of  a  class  at  any 
two  periods — though  undoul)tcdly  this  is  one  and  perhaps  the 
most  important  element  in  striking  a  balance — but  we  ought 
to  compare  all  the  members,  high  and  low,  at  the  two  periods: 
At  an  ancient  epoch  the  highest  and  lowest  mollusks,  namely, 
cephalopods  an(l  brachiopods,  swarmed  in  numbers  ;  at  the  pres- 
sent  tim(^  both  ordei*s  are  greatly  reduced,  while  other  orders, 
intermediate  in  organization,  have  largely  increased;  conse- 
quently some  naturalists  maintain  that  mollusks  were  formerly 
more  highly  developed  than  at  present ;  but  a  stronger  case 
Clin  be  made  out  on  the  opposite  side,  by  considering  the  vast 
reduction  of  the  lowest  mollusks,  and  the  fact  that  our  existing 
cephalopods,  though  few  in  nimibcr,  arc  more  highh''  organized 
than  their  ancient  representatives.  We  ought  also  to  compare 
the  relative  proportional  numbers  of  the  high  and  low  classes 
throughout  the  world  at  any  two  periods :  if,  for  instance,  at 
the  present  day  fifty  thousand  kinds  of  A-ertebrate  animals  ex- 
ist, and  if  we  knew  that  at  some  former  period  only  ten  thou- 
sand kinds  existed,  we  ought  to  look  at  this  increase  in  num- 
ber in  the  highest  class,  which  implies  a  great  displacement  of 
lower  forms,  as  a  decided  advance  in  the  org-anization  of  the 
world.  AVe  thus  see  how  hopelessly  dillicnlt  it  is  to  compare 
with  perfect  fairness,  under  such  extremely  complex  relations, 
tlw;  standard  of  organization  of  the  imperfectly-known  faunas 
of  successive  j^eriods. 

We  shall  apjireciatc  this  difficnlly  the  more  cleaily,  by 
looking  to  certain  existing  faimas  and  iioras.  From  the  extraor- 
dinary manner  in  which  European  productions  have  recently 
spread  over  New  Zealand,  and  have  seized  on  places  whicli 
must  have  lieen  previously  occupied,  we  must  believe  that,  if 
nil  the  animals  and  plants  of  Great  Britain  were  set  free  in 
New  Zeahuul,  in  the  course  of  time  a  multitude  of  ]3ritish  forms 
would  become  thoroughly  naturaliz("d  there,  and  would  exter- 
minate many  of  the  natives.  On  the  other  hand,  from  hardly  a 
single  inhabitant  of  the  southern  hemisphere  having  become 
Anld  in  any  jiart  of  Emope,  we  may  well  doubt  whether,  if  all 
the  productions  of  New  Zealand  vicrc  set  free  in  Great  Britain, 


310  SUCCESSION  OF  THE  Cuap.  X. 

any  considcriiblc  number  -would  be  enabled  to  seize  on  jilaces 
now  occupied  by  our  native  plants  and  animals.  Under  this 
point  of  view,  the  productions  of  Great  Britain  stand  much 
hioher  in  the  scale  than  those  of  New  Zealand.  Yet  the  most 
skilful  naturalist,  from  an  examination  of  the  species  of  the  two 
countries  could  not  have  foreseen  this  result. 

Agassiz  and  several  other  hif^hly-competent  judges  insist 
that  ancient  animals  resemble  to  a  certain  extent  the  embryos 
of  recent  animals  belonging  to  the  same  classes ;  and  that  the 
geological  succession  of  extinct  forms  is  nearly  parallel  Avith 
the  embryological  development  of  existing  forms.  This  view 
accords  admirably  well  with  our  theory.  In  a  future  chapter  I 
shall  attempt  to  show  that  the  adult  differs  from  its  embryo, 
OM'ing  to  variations  supervening  at  a  not  early  age,  and  being 
inherited  at  a  corresponding  age.  This  process,  while  it  leaves 
the  embryo  almost  unaltered,  continually  adds,  in  the  course 
of  successive  generations,  more  and  more  difference  to  the  adult. 
Thus  the  embryo  comes  to  be  left  as  a  sort  of  picture,  preserved 
by  Nature,  of  the  ancient  and  less  modified  condition  of  the 
animal.  This  view  may  be  true,  and  yet  may  never  be  capable 
of  full  proof.  Seeing,  for  instance,  that  the  oldest  known  mam- 
mals, reptiles,  and  fishes,  strictly  belong  to  their  proper  classes, 
though  some  of  these  old  forms  are  in  a  slight  degree  less  dis- 
tinct from  each  other  than  are  the  typical  members  of  the  same 
groups  at  the  present  day,  it  would  be  vain  to  look  for  animals 
having  the  common  embryological  character  of  the  Yertebrata, 
until  beds  rich  in  fossils  are  discovered  far  beneath  the  lowest 
Silurian  stratum — a  discovery  of  which  the  chance  is  small. 

On  the  Succession  of  the  same  Types  xcitJtin  the  same  Areas, 
during  the  later  Tertiary  Periods. 

Mr.  Clift  many  years  ago  showed  that  the  fossil  mammals 
from  the  Australian  caves  were  closely  allied  to  the  living  mar- 
supials of  that  continent.  In  South  America,  a  similar  relation- 
ship is  manifest,  even  to  an  uneducated  eye,  in  the  gigantic 
pieces  of  armor,  like  those  of  tlie  armadillo,  found  in  several 
parts  of  I^a  Plata ;  and  Prof.  Owen  has  shown  in  the  most 
striking  manner  that  most  of  the  fossil  manmials,  buried  there 
in  such  lunnbers,  are  related  to  South  American  t^-pes.  This 
relationship  is  even  more  clearl}'  seen  in  the  wonderful  collection 
of  fossil  bones  made  by  MM.  Lund  and  Clausen  in  the  caves  of 
Urazil.     I   was  so  much    injprcssed    with    these   facts  that  I 


Chap.  X.  SAME  TYPES  IN  THE  SAME  AREAS.  317 

stroni^ly  insisted,  in  1839  and  1845,  on  tliis  "  law  of  the  suc- 
cession of  types,"  on  "  tliis  -wonderful  relationship  in  the  same 
continent  between  the  dead  and  the  livinrr."  Prof.  Owen  has 
subsecjuentlv  extended  the  same  ^"eneralization  to  tlie  mammals 
of  the  Old  World.  We  see  the  same  law  in  this  author's  res- 
torations of  the  extinct  and  ^ijj^antic  birds  of  New  Zealand. 
We  see  it  also  in  the  birds  of  the  caves  of  Brazil.  Mr.  ^V^)^)d- 
ward  has  shown  that  the  same  law  holds  good  with  sea-shells, 
but,  from  the  wide  distribution  of  most  genera  of  mollusks,  it 
is  not  well  dis})layed  by  them.  Other  cases  could  be  added,  as 
the  relation  between  the  extinct  and  living  land-shells  of  Ma- 
deira ;  and  between  the  extinct  and  living  brackish-water  shells 
of  the  Aralo-Casjiian  Sea. 

Now  what  does  this  remarkable  law  of  the  succession  of 
the  same  types  within  the  same  areas  mean  ?  He  would  be  a 
bold  man,  who,  after  comparing  the  present  climate  of  Aus- 
tralia and  of  parts  of  South  America  under  the  same  lati- 
tude, would  attempt  to  account,  on  the  one  hand,bv  dissimilar 
physical  conditions,  for  the  dissimilarity  of  the  inhabitants  of 
these  two  continents,  and,  on  the  other  hand,  by  similarity  of 
conditions,  for  the  uniformity  of  the  same  types  in  each  during 
the  later  tertiary  periods.  Nor  can  it  be  pretended  that  it  is 
an  immutable  law  that  marsupials  should  have  been  chiefly  or 
solely  produced  in  Australia;  or  that  Edentata  and  otln^r 
American  types  should  have  been  solely  produced  in  South 
America.  For  we  know  that  Europe  in  ancient  times  was 
peopled  by  numerous  marsupials  ;  and  I  have  shown,  in  the 
])ublications  above  alluded  to,  that  in  America  the  law  of  dis- 
tribution of  terrestrial  matnmals  was  foniierly  dillV-rent  from 
what  it  now  is.  North  America  formerly  partook  strongly  of 
the  present  character  of  the  southern  half  of  the  continent ; 
and  the  southern  half  was  formerly  more  closely  allied,  than  it 
is  at  present,  to  the  northern  half.  In  a  similar  manner  we 
know,  from  Falconer  and  Cautley's  discoveries,  that  Northern 
India  was  formerly  more  closely  related  in  its  mammals  to 
Africa  than  it  is  at  the  present  time.  Analogous  facts  could 
be  given  in  relation  to  the  distribution  of  marine  animals. 

On  the  theory  of  descent  with  modillcation,  the  great  law 
of  the  long-enduring,  but  not  inmiutable,  succession  of  the 
same  t^'pes  within  the  same  areas,  is  at  onct;  explained;  for  the 
inhabitants  of  each  <|uarter  of  tin;  world  will  obviously  tend  to 
leave  in  that  quarter,  during  the  next  succeeding  period  of 
time    closely-allied  though  in  some  degree  modified  descend 


318  SUMMAKY  OF  THE  Cuap.  X. 

ants.  If  llio  inhabitants  of  one  continent  formerly  differed 
greatly  from  those  of  another  continent,  so  will  their  modified 
descendants  still  dillcr  in  nearly  the  same  manner  and  degree, 
lint  after  very  long  intervals  of  time,  and  after  great  geo- 
graphical changes,  permitting  much  inter-migration,  the  fee- 
bler will  yield  to  the  more  dominant  forms,  and  there  will  be 
nothing  innnutable  in  the  laws  of  past  and  present  distribu- 
tion. 

It  may  be  asked  in  ridicule,  whctlier  I  suppose  tliat  the 
megatherium  and  other  allied  huge  monsters,  which  formerly 
lived  in  South  America,  have  left  behind  them  the  sloth,  arma- 
dillo, and  anteater,  as  their  degenerate  descendants.  This  can- 
not for  an  instant  be  admitted.  These  huge  animals  have 
become  wlioll^'^  extinct,  and  have  left  no  progeny.  But  in  the 
caves  of  Brazil,  there  are  many  extinct  species  Avhich  are  close- 
ly allied  in  size  and  in  all  other  characters  to  the  species  still 
liv-ing  in  South  America  ;  and  some  of  these  fossils  may  be  the 
actual  progenitors  of  living  species.  It  must  not  be  forgotten 
that,  on  our  theory,  all  the  species  of  the  same  genus  are  the 
descendants  of  some  one  species;  so  that,  if  six  genera,  each 
having  eight  species,  be  found  in  one  geological  formation,  and 
in  a  succeeding  formation  there  be  six  other  allied  or  repre- 
sentative genera  each  Avith  the  same  number  of  species,  then  we 
may  conclude  that  generally  only  one  species  of  each  of  the 
older  genera  has  left  modified  descendants,  which  constitute 
the  several  species  of  the  new  genera ;  the  other  seven  species 
of  each  old  genus  ha^ang  died  out  and  left  no  progeny.  Or, 
and  this  probably  will  be  a  far  commoner  case,  two  or  three 
species  in  two  or  three  alone  of  the  six  older  genera  will  be 
the  parents  of  the  new  genera :  the  other  species  and  the 
other  whole  genera  having  become  utterly  extinct.  In  failing 
ordcre,  with  the  genera  and  species  decreasing  in  numbers,  as 
is  the  case  with  the  Edentata  of  South  America,  still  fewer 
genera  and  species  will  leave  modified  blood-descendants. 

Summary  of  the  preceding  andprese7it  Chapter. 

I  have  attempted  to  show  that  the  geological  record  is  ex- 
tremely imperfect ;  that  only  a  small  portion  of  the  globe  has 
been  geologically  explored  with  care  ;  that  only  certain  class- 
es of  organic  beings  have  been  largely  preserved  in  a  fossil 
state;  that  the  number  both  of  specimens  and  of  species,  pre- 
served in  our  museums,  is  absolutely  as  notliing,  compared 


CiiAi".  X.  PRKCKDING   AND   PKESENT  CHAPTER.  319 

with  the  number  of  p^encralions  which  must  have  iiasscd  away 
even  during  a  siii<:;le  formation;  lliat,  owinfj;'  to  subsidence 
being  ahuost  necessary  for  the  accumulation  of  deposits  rich  in 
fossil  species  of  very  many  kinds  and  thick  enough  to  resist  fu- 
ture degradation,  great  intervals  of  time  must  have  elapsed 
between  most  of  our  successive  formations;  that  there  has 
probably  been  more  extinction  during  the  periods  of  subsi- 
dence, and  more  variation  during  tlie  periods  of  elevation, 
and  during  the  latter  the  record  will  have  been  least  perfectly 
kept ;  that  each  single  formation  has  not  been  continuously 
deposited;  that  tlH>  duration  of  each  formation  is,  probably, 
short  compared  with  the  average  duration  of  specidc  forms ; 
that  migration  has  played  an  important  part  in  the  first  ap- 
pearance of  now  forms  in  any  one  area  and  fonnation ;  that 
widely-ranging  species  are  those  which  have  varied  most  fre- 
quently, and  have  oftenest  given  rise  to  new  species  ;  that  va- 
rieties have  at  first  been  local ;  and  lastly,  although  each  spe- 
cies must  have  j^asscd  through  numerous  transitional  stages,  it 
is  probable  that  the  periods,  during  which  each  underwent 
modification,  though  many  and  long  as  measured  l)y  years, 
have  been  short  in  comparison  with  the  periods  during  which 
each  remained  in  an  unchanged  condition.  These  causes,  taken 
conjointly,  will,  to  a  large  extent,  explain  why — though  we  do 
find  many  links — we  do  not  find  interminable  varieties,  con- 
necting together  all  extinct  and  existing  forms  liy  the  finest 
graduated  steps.  It  should  also  be  constantly  borne  in  mind 
that  any  linking  varieties  between  two  or  more  forms,  which 
might  be  found,  would  be  ranked,  unless  the  whole  chain  could 
be  perfectly  restored,  as  so  many  new  and  disthict  species  ;  for 
it  is  not  pretended  that  we  have  any  sure  criterion  by  which 
species  and  varieties  can  be  discriminated. 

H(!  who  rejt;cts  these  views  on  the  imperfection  of  tlie  geo- 
logical record,  will  rightly  reject  the  whole  theory.  For  he 
may  ask  in  vain  where  are  the  numberless  transitional  links 
which  must  formerly  have  connected  the  closely-allied  or  rep- 
resentative species  found  in  the  successive  stages  of  the  same 
great  formation  ?  lie  may  disbelieve  in  the  immense  intervals 
of  time  which  have  elapsed  between  our  consecutivt;  forma- 
tions ;  he  may  overlook  how  important  a  part  migration  has 
tjlaycd,  when  the  fonnations  of  any  one  gieat  region  alone,  as 
that  of  Europe,  are  considen-d  ;  he  may  urge  the  apparent,  but 
often  falsely  appanMit,  sudden  coming  in  of  whole  groups  of 
species.    He  may  ask  where  are  the  remains  of  those  infinitely- 


3J0  SUMMARY  OF  THE  Chap.  X. 

numerous  or<Tanisnis  wliicli  must  have  existed  long  before  the 
Cambrian  system  ^vas  deposited  ?  We  now  know  that  at  least 
one  animal  did  then  exist ;  but  I  can  answer  the  above  ques- 
tion only  l)y  supjiosin<^  that  where  our  oceans  now  extend  tliey 
have  extended  for  an  enormous  .period,  and  wliere  our  oscillat- 
ing continents  now  stand,  they  have  stood  since  the  coinmence- 
mcnt  of  the  Cambrian  system ;  but  that,  long  before  that 
epoch,  the  world  presented  a  Avidcly-diirerent  aspect ;  and  that 
the  older  continents,  formed  of  formations  older  than  any 
known  to  us,  exist  now  only  as  remnants  in  a  metamorphosed 
condition,  or  he  still  buried  under  the  ocean. 

Passing  from  these  difficulties,  the  other  great  leading 
facts  in  paleontology  seem  to  me  simply  to  follow  on  the  the- 
ory of  descent  with  modification  through  natural  selection. 
We  can  thus  understand  how  it  is  that  new  species  come  in 
slowly  and  successively ;  how  species  of  different  classes  do 
not  necessarily  change  together,  or  at  the  same  rate,  or  in  the 
same  degree ;  yet  in  the  long-run  that  all  undergo  modification 
to  some  extent.  The  extinction  of  old  forms  is  the  almost 
inevitable  consequence  of  the  production  of  new  fonns.  We 
can  imderstand  Avhy  Avhcn  a  species  has  once  disappeared  it  nev- 
er reappears.  Groups  of  species  increase  in  numbers  slowly, 
and  endure  for  unequal  periods  of  time ;  for  the  process  of 
modification  is  necessarily  slow,  and  depends  on  many  com- 
plex contingencies.  The  dominant  species  belonging  to  large 
and  dominant  groups  tend  to  leave  many  modified  descend 
ants,  which  form  new  sub-groups  and  groups.  As  these  are 
formed,  the  species  of  the  less  vigorous  groups,  from  their  infe- 
riority inherited  from  a  common  progenitor,  tend  to  become 
extinct  together,  and  to  leave  no  modified  oQ'spring  on  the  face 
of  the  earth.  But  the  utter  extinction  of  a  whole  group  of 
species  has  sometimes  been  a  slow  process,  from  the  surnval 
of  a  few  descendants,  lingering  in  protected  and  isolated  situ- 
ations. When  a  group  has  once  wholly  disappeared,  it  does 
not  reappear;  for  the  link  of  generation  has  been  broken.     - 

AVe  can  understand  how  the  dominant  fonns  which  spread 
widel}'  and  yield  the  ;;Teatest  number  of  varieties  Avill  tend  to 
people  the  world  with  allied,  but  modified,  descendants ;  and 
these  will  generally  succeed  in  displacing  the  groups  which  are 
their  inferiors  in  the  struggle  for  existence.  Hence,  after  long 
intervals  of  time,  the  jiroductions  of  the  world  apjicar  to  have 
changed  sinmltaneously. 

We  can  understand  how  it  is  that  all  the  forms  of  life 


CiiAP.  X.  PRECEDING  AND  PRESENT  CHAPTER.  321 

ancient  and  recent,  make  tog-ctlier  a  (c\v  f^rand  classes  ;  for  all 
arc  at  least  thus  far  connected  by  generation.  We  can  undci'- 
stand,  from  the  continued  tendency  to  divergence  of  character, 
why  the  more  ancient  a  form  is,  the  more  it  gcnc^rally  differs 
from  those  now  living;  why  ancient  and  extinct  forms  often 
tend  to  fill  up  gaps  between  existing  forms,  sometimes  blend- 
ing two  groups,  previously  classed  as  •  distinct,  into  one ;  but 
more  connnonly  bringing  them  only  a  little  closer  together. 
The  more  ancient  a  form  is,  the  more  often  it  stands  in  some 
degree  intermediate  between  groups  now  distinct;  for  the 
more  ancient  a  form  is,  the  more  nearly  it  will  be  related  to, 
and  consequently  resemble,  the  common  progenitor  of  groups, 
since  become  widely  divergent.  Extinct  forms  are  seldom  direct- 
ly intermediate  between  existing  forms  ;  but  are  intermcfhate 
onl}'  by  a  long  and  circuitous  course  through  other  extinct  and 
difl'erent  forms.  We  can  clearly  sec  why  the  organic  remains  of 
closely-consecutive  formations  are  closely  allied  ;  for  they  are 
closely  linked  togetlier  by  generation.  ^Ve  can  clearly  see  why 
the  remains  of  an  intermediate  formation  are  intermediate  in 
cliaracter. 

The  inhabitants  of  each  successive  period  in  the  world's 
history  must  have  beaten  their  predecessors  in  the  race  for  life, 
and  are,  in  so  far,  higher  in  the  scale  of  Nature,  and  tlieir 
structure  has  generally  become  more  specialized  ;  and  this  may 
account  for  the  common  belief  held  by  so  many  paleontolo- 
gists, that  organization  on  the  whole  has  progressed.  Extinct 
and  ancient  animals  resemble  to  a  certain  extent  the  embryos 
of  the  more  recent  animals  belonging  to  the' same  classes,  and 
this  wonderful  fact  receives  a  simple  explanation  according  to 
our  views.  The  succession  of  the  same  types  of  structure  with- 
in the  same  areas  during  the  later  geological  periods  ceases  to 
be  mysterious,  and  is  intelligible  on  the  principle  of  inlierit- 
ancc. 

If,  then,  the  geological  record  be  as  imperfect  as  many  be- 
lieve, and  it  may  at  least  be  asserted  that  the  record  cannot  be 
jiroved  to  be  much  more  perfect,  the  main  ol)jections  to  the 
theory  of  natural  selection  are  greatly  diminished  or  disappear. 
On  the  other  hand,  all  the  chief  laws  of  paleontology  plainly 
jiroflaim,  as  it  seems  to  me,  that  species  have  been  produced 
by  ordinary  generation:  old  forms  having  been  supjilanted  by 
new  and  imjjroved  forms  of  life,  the  products  of  Variation  and 
the  Survival  of  the  Fittest. 


322  GEOGKAPIIICAL  DISTRIBUTION.  Cuai-.  XI. 


CHAPTER  XI. 

GKOGRAPIIICAL    DISTKiCUTION. 

f  resent  Distribution  cnnnot  be  accounted  for  by  Differences  in  Phj-sical  Conditions 
— Importance  of  Barriers — Afllniiy  of  the  Prodnctiotis  of  the  same  Continent — 
Centres  of  Creation — Means  of  Dispersal  by  Changes  of  Climate  and  of  the  Level 
of  the  Land,  and  by  Occasional  Means — Dispersal  during  the  Glacial  Period — 
Alternate  Glacial  Periods  in  the  North  and  South. 

In'  considering  the  distribution  of  organic  beings  over  the 
face  of  the  globe,  the  first  great  fact  which  strikes  us  is,  that 
neither  the  similarity  nor  the  dissimilarity  of  the  inhabitants 
of  various  regions  can  be  accoimted  for  by  their  climatal  and 
other  jihysical  conditions.  Of  late,  almost  every  author  who 
has  studied  the  subject  has  come  to  this  conclusion.  The  case 
of  America  alone  would  almost  sulllce  to  prove  its  truth  :  for,  if 
we  exclude  th.e  northern  parts  where  the  circumpolar  land  is 
almost  continuous,  all  authors  agree  that  one  of  the  most  fun- 
damental divisions  in  geographical  distribution  is  that  between 
the  New  and  Old  Worlds ;  yet,  if  Ave  travel  over  the  vast 
American  Continent,  from  the  central  parts  of  the  United 
States  to  its  extreme  southern  point,  we  meet  with  tin; 
most  diversified  conditions  ;  liinnid  districts,  arid  deserts,  lofty 
moimtains,  grassy  plains,  forests,  marshes,  lakes,  and  great 
rivers,  under  almost  every  temperature.  Tlierc  is  hardly  a 
climate  or  condition  iii  the  Old  World  which  cannot  be  paral- 
leled in  the  New — at  least  as  closely  as  the  same  species  gen- 
erally require.  No  doubt  small  areas  can  be  jiointed  out  in 
the  Old  A\''orld  hotter  than  any  in  the  New  A^'orld,  but  these 
are  not  inhabited  by  a  fauna  different  from  that  of  the  sur- 
rounding districts ;  for  it  is  very  rare  to  find  a  group  of  organ- 
isms conilned  to  a  small  area,  having  conditions  peculiar  in 
only  a  slight  degree.  Notwithstanding  this  general  parallel- 
ism in  the  conditions  of  the  Old  and  New  Worlds,  how  widely 
different  are  their  living  productions! 

In  tho  southern  hemisphere,  if  wc  compare  large  tracts  of 


CuAP.  XI.  GEOGRAPHICAL  DISTRIBUTION.  323 

land  in  Australia,  South  Africa,  and  Western  South  America, 
between  latitudes  20"^  and  35°,  we  shall  find  parts  extremely 
similar  in  all  their  conditions,  yet  it  would  not  he  possible  to 
point  out  three  faunas  and  floras  more  utterly  dissimilar.  Or 
again,  we  may  compare  the  productions  of  South  America 
south  of  hit,  35°  with  those  north  of  25°,  which  consequently 
are  separated  by  a  space  of  ten  deg'rces  of  latitude  and  are  ex- 
posed to  considerably  different  conditions,  yet  they  are  incom- 
I)arably  more  closely  related  to  each  other  than  they  arc  to  the 
productions  of  Australia  or  Africa  under  nearly  the  same  cli- 
mate. Analog'ous  facts  could  be  given  with  respect  to  the 
inhabitants  of  the  sea. 

A  second  great  fact  which  strikes  us  in  our  general  review 
is,  that  barriers  of  any  kind,  or  obstacles  to  free  migration,  are 
related  in  a  close  and  important  manner  to  the  differences  be- 
tween the  productions  of  various  regions.  We  sec  this  in  the 
great  difference  of  nearly  all  the  terrestrial  productions  of  the 
New  and  Old  Worlds,  excepting  in  the  northern  parts,  Avhere 
the  land  almost  joins,  and  where,  under  a  slightly-different  cli- 
mate, there  might  have  been  free  mij^Tation  for  the  northern 
temperate  forms,  as  there  now  is  for  the  strictly  arctic  produc- 
tions. We  see  the  same  fact  in  the  great  difference  betwefMi 
the  inhabitants  of  Australia,  Africa,  and  South  America,  under 
the  same  latitude :  for  these  countries  are  almost  as  much  iso- 
lated from  each  other  as  is  possible.  On  each  continent,  also, 
we  see  the  same  fact ;  for,  on  the  opposite  sides  of  lofty  and 
continuous  mountain-ranges,  of  great  deserts,  and  even  of  large 
rivers,  we  find  different  productions ;  though  as  mountain- 
chains,  deserts,  etc.,  are  not  as  impassable,  or  likely  to  have 
endured  so  long,  as  the  oceans  separating  continents,  the  differ- 
ences are  very  inferior  in  degree  to  those  characteristic  of  dis- 
tinct continents. 

Turning  to  the  sea,  we  find  the  same  law.  The  marine  in- 
habitants of  the  eastern  and  western  shores  of  South  America 
arc  very  distinct,  with  extremely  few  fishes,  shell,  or  crabs,  in 
common  ;  but  Dr.  GUnther  has  recently  shown  that  on  opjio- 
site  sides  of  the  Isthmus  of  Panama,  about  thirty  jier  cent,  of 
the  fishes  are  the  same  ;  and  this  fact  has  led  naturalists  to  be- 
lieve that  the  istlnnus  was  formerly  open.  Westward  of  the 
shores  of  America,  a  wide  space  of  open  ocean  extends,  with 
not  an  island  as  a  hahing-place  for  emigrants  ;  here  we  have  a 
barrier  of  another  kind,  and  as  soon  as  this  is  passed  we  meet 
in  the  eastern  islands  of  the  Pacilic  with  another  and  totally 


324  GKOGKAPIIICAL  DISTRIBUTION.  Chap.  XI. 

distinct  fauna.  So  that  three  marine  faunas  range  far  north- 
ward and  southward  in  parallel  lines  not  far  from  each  other, 
imder  corrcspondini^  climates ;  but  from  beinf^  separated  from 
each  other  by  impassable  barriers,  either  of  land  or  open  sea, 
they  are  almost  wholly  distinct.  On  the  other  hand,  proceed- 
ing still  farther  westward  from  the  eastern  islands  of  the  tropi- 
cal parts  of  the  Pacific,  we  encounter  no  impassable  barriers, 
and  we  have  innumerable  islands  as  halting--places,  or  continu- 
ous coasts,  imtil  after  travelling  over  a  hemisphere  we  come  to 
the  shores  of  Africa  ;  and  over  this  vast  space  we  meet  witli 
no  well-defined  and  distinct  marine  faunas.  Although  so  few 
shells,  crabs,  or  fishes,  arc  common  to  the  above-named  three 
approximate  faunas  of  Eastern  and  Western  America  and  the 
eastern  Pacific  islands,  yet  many  fish  range  from  the  Pacific 
into  the  Indian  Ocean,  and  many  shells  are  common  to  the 
eastern  islands  of  the  Pacific  and  the  eastern  shores  of  Africa, 
on  almost  exactly  opposite  meridians  of  longitude. 

A  third  great  fact,  partly  included  in  the  foregoing  state- 
ment, is  the  ailinity  of  the  productions  of  the  same  continent, 
or  of  the  same  sea,  though  the  species  themselves  are  distinct 
at  different  points  and  stations.  It  is  a  law  of  the  widest 
generality,  and  every  continent  offers  innumerable  instances. 
Nevertheless  the  naturalist,  in  travelling,  for  instance,  from 
north  to  south,  never  fails  to  be  struck  by  the  manner  in  which 
successive  groups  of  beings,  specifically  distinct,  nearly  related, 
replace  each  other.  He  hears  from  closely-allied,  yet  distinct 
kinds  of  birds,  notes  nearly  similar,  and  sees  their  nests  simi- 
larly constructed,  but  not  quite  alike,  with  eggs  colored  in 
nearly  the  same  manner.  The  plains  near  the  Straits  of  Magel- 
lan are  inhabited  by  one  species  of  Rhea  (American  ostrich), 
and  northward  the  plains  of  La  Plata  by  another  species  of  the 
same  genus  ;  and  not  by  a  true  ostrich  or  emu,  like  those  in- 
habiting Africa  and  Australia  imdcr  the  same  latitude.  On 
these  same  plains  of  La  Plata,  we  see  the  agouti  and  bizcacha, 
animals  having  nearly  the  same  habits  as  our  hares  and  rabbits 
and  belonging  to  the  same  order  of  Rodents,  but  they  plainly 
display  an  American  type  of  structure.  We  ascend  the  lofty 
peaks  of  the  Cordillera,  and  we  find  an  alpine  species  of  biz- 
cacha ;  we  look  to  the  waters,  and  we  do  not  find  the  beaver 
or  nuisk-rat,  but  the  coypu  and  capybara,  rodents  of  the  South 
Americaii  ty\)C.  Inmunerable  other  instances  could  be  given. 
If  we  look  to  the  islands  off  the  American  shore,  however  much 
they  may  differ  in  geological    structure,  the  inhabitants  are 


Chap.  XI.  GEOGRAPHICAL  DISTRIBUTION.  305 

(>sscnlially  Aniorlcan,  though  they  may  be  all  peculiar  species. 
We  may  look  back  to  past  ages,  as  shown  in  tli(j  last  chapter, 
and  we  lind  American  types  then  prevailing  on  the  American 
Continent  and  in  the  American  seas.  AVe  see  in  these  fact.s 
some  deep  organic  bond,  throughout  space  and  time,  over  the 
same  areas  of  land  and  water,  and  indej)endent  of  physical  con- 
ditions. The  naturalist  must  be  dull  who  is  not  led  to  inquire 
•what  this  bond  is. 

The  bond  is  simply  inheritance,  that  cause  which  alone,  as 
far  as  we  positive!}'  know,  produces  organisms  quite  Hke  each 
other,  or,  as  we  see  in  the  case  of  varieties,  nearly  alike.  The 
dissimilarity  of  the  inhabitants  of  different  regions  may  be  at- 
trilnited  to  modification  througli  natural  selection,  and  in  a 
subordinate  degree  to  the  definite  inlluence  of  different  phys- 
ical conditions.  The  degree  of  dissimilarity  will  depend  on 
the  migration  of  the  more  dominant  forms  of  life  from  one  re- 
gion into  another  having  been  prevented  more  or  less  effectually, 
at  periods  more  or  less  remote — oii  the  nature  and  number  of 
the  former  inmiigrants — and  on  the  action  of  the  inhabitants 
on  each  other  in  leading  to  the  preservation  of  different  modifi- 
cations; the  relation  of  organism  to  organisin  in  the  struggle 
for  life  being,  as  I  have  already  often  remarked,  the  most  im- 
portant of  all  relations.  Thus  the  high  importance  of  barriers 
comes  into  play  by  checking  migration ;  as  does  time  for  the 
slow  process  of  modification  througli  natural  selection.  Widely- 
ranging  species,  abounding  in  individuals,  which  have  already 
triumphed  over  many  competitors  in  their  own  widelj'-extendcd 
homes,  will  have  the  best  chance  of  seizing  on  new  places,  when 
they  spread  into  new  countries.  In  their  new  homes  they  will 
be  exposed  to  new  conditions,  and  will  fre(iuently  undergo 
further  modification  and  improvement ;  and  thus  they  will  be- 
come still  further  victorious,  and  will  produce  grou[is  of  modi- 
fied descendants.  On  this  principle  of  inheritance  with  modili- 
eation,  we  can  uiidci-stand  how  it  is  that  sections  of  genera, 
whole  genera,  and  even  families,  are  confined  to  the  same  areas, 
as  is  so  commonly  and  notoriously  the  case. 

I  believe,  as  was  remarked  in  the  last  chapter,  in  no  law  of 
necessary  d(?velopment.  As  the  variability  of  each  species  is 
an  independent  property,  and  will  Ix;  taken  advantage  of  by 
natural  selection,  only  so  far  as  it  jirolits  each  individual  in  its 
complex  struggle  for  life,  so  the  amount  of  modification  in 
difierent  species  Avill  be  no  uniform  (juantity.  If  a  number  of 
species,  after  having  long  conipeteil  witli  each  otlier  in  their 


32G  SINGLE  CENTRES  OF  CREATION.  Chap.  XI. 

old  home,  were  to  mi^^atc  in  a  body  into  a  new  and  afterward 
isolated  country,  they  Avould  be  little  liable  to  modification ; 
for  n('itli(>r  niig-ration  nor  isolation  in  themselves  can  effect  any 
tiling.  These  principles  come  into  play  only  by  bringin*:^  or- 
ganisms into  new  relations  with  each  other,  and  in  a  lesser  de- 
gree Avith  the  surrounding  physical  conditions.  As  we  have 
seen  in  the  last  chai)tcr  that  some  forms  have  retained  nearly 
the  same  character  from  an  enormously  remote  geological 
period,  so  certain  s})ecies  have  migrated  over  vast  spaces,  and 
have  not  become  greatly  or  at  all  modified. 

According  to  these  views,  it  is  obvious  that  the  several 
species  of  the  same  genus,  though  inhabiting  the  most  distant 
quarters  of  the  world,  must  originally  have  proceeded  from  the 
same  source,  as  they  are  descended  from  the  same  progenitor. 
In  the  case  of  those  species,  which  have  undergone  during 
whole  geological  periods  but  little  modification,  there  is  not 
much  difficulty  in  believing  that  they  may  have  migrated  from 
the  same  region ;  for,  during  the  vast  geographical  and  climatid 
changes  which  have  supervened  since  ancient  times,  almost 
any  amount  of  migration  is  possible.  But  in  many  other  cases, 
in  Avhich  we  have  reason  to  believe  that  the  species  of  a  genus 
have  been  produced  within  comparatively  recent  times,  there  is 
great  difficulty  on  this  head.  It  is  also  obvious  that  the  individ- 
uals of  the  same  species,  though  now  inhabiting  distant  and 
isolated  regions,  must  have  proceeded  from  one  spot,  where 
their  parents  were  lirst  produced:  for,  as  explained  in  the  last 
chajiler,  it  is  incredible  that  individuals  identically  the  same 
should  have  been  produced  from  parents  specifically  distinct. 

Single  Centres  of  supposed  Creation. — We  are  thus  brought 
to  the  question  which  has  been  largely  discussed  by  naturalists, 
namely,  whether  species  have  beeia  created  at  one  or  more 
points  of  the  earth's  surface.  Undoubtedly  there  are  many 
cases  of  extreme  difficulty  in  understanding  how  the  same  species 
could  possibly  have  migrated  from  some  one  point  to  the  several 
distant  and  isolated  points  where  noAV  found.  Nevertheless  the 
simplicity  of  the  view  that  each  species  was  first  produced 
within  a  single  region  captivates  the  mind.  lie  Avho  rejects  it, 
rejects  the  vera  causa  of  ordinary  generation  with  subsequent 
migration,  and  calls  in  the  agency  of  a  miracle.  It  is  univer- 
sally admitted  that  in  most  cases  the  area  inhabited  by  a  spe- 
cies is  continuous ;  and  that  when  a  plant  or  animal  inhabits 
two  points  so  distant  from  each  other,  or  with  an  interval  of 
such  a  nature,  that  the  space  could  not  be  easily  passed  over 


CuAP.  XI.  SINGLE  CENTRES  OF  CREATION.  .        327 

by  mip^raliun,  the  fact  is  g'iv^cn  as  something  njiiarkablc  and 
exceptional.  The  incapacity  of  migrating  across  a  wide  sea  is 
more  clear  in  the  case  of  terrestrial  mannnals  than  perhaps  with 
any  other  organic  beings;  and,  accordingly,  Ave  iind  no  inex- 
plicable instances  of  the  same  mammals  inhabiting  distant 
points  of  the  world.  No  geologist  feels  any  dilliculty  in  Great 
Britain  possessing  tlu^  same  (juadrupeds  with  the  rest  of  Europe, 
for  they  were  no  doubt  once  united.  But  if  the  same  species 
can  be  produced  at  two  separate  points,  why  do  we  not  find  a 
single  mammal  common  to  Europe  and  Australia  or  Soutlx 
America  ?  The  conditions  of  life  are  nearly  the  same,  so  that 
a  multitude  of  European  animals  and  plants  have  become  nat- 
uralized in  America  and  Australia;  and  some  of  the  aboriginal 
plants  are  identically  the  same  at  these  distant  points  of  the 
northern  and  southern  hemispheres  ?  The  answer,  as  I  believe, 
is,  that  mammals  have  not  been  able  to  migrate,  whereas  some 
]>lants,  from  their  varied  means  of  disp(>rsal,  have  migrated 
across  the  wide  and  broken  interspaces.  The  great  and  striking 
influence  of  barriers  of  all  kinds  is  intelligible  only  on  the  view 
that  the  great  majority  of  species  have  been  produced  on  one 
side,  and  have  not  been  able  to  migrate  to  the  opposite  side. 
Some  few  families,  many  sub-families,  very  many  genera,  and  a 
still  greater  number  of  sections  of  genera,  are  conlined  to  a  sin- 
gle region  ;  and  it  has  been  oljserved  by  several  naturalists  that 
the  most  natural  genera  or  those  genera  in  whicii  the  species  are 
most  closely  related  to  each  other,  are  generally  confined  to  the 
same  countr}',  or  if  they  have  a  wide  range  that  their  range 
is  continuous.  What  a  strange  anomaly  it  woidd  be,  if  a  di- 
rectly opposite  rule  were  to  prevail,  when  we  go  down  one  step 
lower  in  the  series,  namely,  to  the  individuals  of  the  same  spe- 
cies, and  these  had  not  been,  at  least  at  first,  confined  to  some 
one  region ! 

Hence  it  seems  to  me,  as  it  has  to  many  other  naturalists, 
that  the  view  of  each  species  having  been  produced  in  one  area 
alone,  and  having  subsequently  migrated  from  that  area  as  far 
as  its  powers  of  migration  and  subsistence  under  past  and  pres- 
ent conditions  permitted,  is  the  most  jirobable.  Undoubtedly 
many  cases  occur,  in  which  we  cannot  explain  how  the  same 
species  could  have  jiassed  from  one  point  to  the  other.  But 
tlic  geographical  and  dimatal  dianges,  which  have  certainly 
occurred  within  recent  geological  times,  nuist  have  rendered 
discontinuous  the  formerly  conliinious  range  of  many  species. 
So  that  we  are  reduced  to  consider  whether  the  exceptions  to 


328        •  SINGLE  CENTKES  OF   CKEATION.  Cii.vr.  XI. 

contiiuiity  of  rani^c  arc  so  numerous  and  of  so  grave  a  nature, 
that  we  ought  to  give  up  the  belief,  rendered  probable  by 
general  considerations,  that  each  species  has  been  produced 
within  one  area,  and  has  migrated  thence  as  far  as  it  could.  It 
^vould  be  hopelessly  tedious  to  discuss  all  the  exceptional  cases 
of  the  same  species,  now  living- at  distant  and  separated  points; 
nor  do  I  for  a  moment  i)retend  that  any  explanation  could  l)c 
olVercd  of  many  instances.  But  after  some  jireliminary  remarks, 
I  will  discuss  a  few  of  the  most  striking  classes  of  facts  ;  namely, 
the  existence  of  the  same  species  on  the  summits  of  distant; 
mountain-ranges,  and  at  distant  points  in  the  arctic  and  ant- 
arctic regions;  and  secondly  (in  the  following  chapter),  tlic 
wide  distribution  of  fresh-water  productions  ;  and  thirdly,  the 
occurrence  of  the  same  terrestrial  species  on  islands  and  on  the 
main-land,  though  separated  by  hundreds  of  miles  of  open  sea. 
If  the  existence  of  the  same  species  at  distant  and  isolated 
points  of  the  earth's  surface,  can  in  many  instances  be  ex- 
plained on  the  view  of  each  species  having  migrated  from  a 
single  birthplace;  then,  considering  our  ignorance  Avith  respect 
to  former  climatal  and  geographical  changes,  and  to  the  various 
occasional  means  of  transport,  the  belief  that  a  single  birthplace 
is  the  law,  seems  to  me  incomparably  the  safest. 

In  discussing  this  subject,  we  shall  be  enabled  at  the  same 
time  to  consider  a  point  equally  important  for  us,  namely, 
whether  the  several  species  of  a  genus,  which  must  on  the 
iheorj-  all  be  descended  from  a  common  progenitor,  can  have 
migrated,  undergoing  modification  during  their  migration,  from 
some  one  area.  When  most  of  the  species  inhabiting  one  re- 
gion are  diflcrcnt  from  those  of  another  region,  but  are  closely 
allied  or  belong  to  the  same  genera,  if  in  all  such  cases  it  can 
be  shown  that  there  probably  has  been  at  some  former  period 
migration  from  the  one  region  to  the  other,  our  general  view 
will  be  much  strengthened ;  for  the  explanation  is  obvious  on 
the  principle  of  descent  with  modification.  A  volcanic  island, 
for  instance,  upheaved  and  fomied  at  the  distance  of  a  few 
hundreds  of  miles  from  a  continent,  would  prol^ably  receive  from 
it  in  the  course  of  time  a  few  colonists,  and  their  descendants, 
though  modified,  would  still  be  related  by  inheritance  to  the 
inhabitants  of  that  continent.  Cases  of  this  nature  are  common, 
and  are,  as  we  shall  hereafter  see,  inexplicable  on  the  tlicory  of 
indi'pendent  creation.  This  view  of  the  relation  of  the  species 
of  one  region  to  those  of  another,  does  not  differ  much  from 
that  advanced  by  Mr.  "Wallace,  who  concludes  that  "  every  spc- 


Chap.  XI.  MEANS  OF  DISPERSAL.  329 

cics  has  come  into  existence  coincident  both  in  sjKice  and  time 
with  a  preexist ino-  closely-allied  species."  And  I  now  know  that 
he  attributes  this  coincidence  to  descent  with  modification. 

The  discussion  on  "  single  and  multiple  centres  of  crea- 
tion "  does  not  directly  l)ear  on  another  allied  question — 
namely,  whether  all  the  individuals  of  the  same  species  are 
descended  from  a  single  pair,  or  single  hermaphrodite,  or 
whether,  as  some  authors  suppose,  from  many  individuals  si- 
uuiltan<'()usly  created.  With  organic  beings  which  never  inter- 
cross, if  such  exist,  each  species  must  be  descended  from  a  suc- 
cession of  modified  varieties,  which  have  sujiplanted  each 
other,  but  which  have  never  blended  with  other  individuals 
or  varieties  of  the  same  species ;  so  that,  at  each  successive 
stage  of  modification  and  improvement,  all  the  individuals 
of  the  same  variety  will  be  descended  from  a  single  parent. 
IJut  in  the  great  majority  of  cases,  namely,  with  all  organisms 
which  habitually  unite  for  each  birth,  or  which  occasionally  inter- 
cross, the  individuals  of  the  same  species  inhabiting  the  same 
area  will  be  kept  nearly  uniform  by  intercrossing;  so  that 
many  individuals  will  go  on  simultaneously  changing,  and  the 
whole  amount  of  modification  at  each  stage  will  not  be  due  to 
descent  from  a  single  parent.  To  illustrate  what  I  mean :  our 
English  race-horses  chfler  from  the  horses  of  every  other  breed ; 
but  they  do  not  owe  their  difference  and  superiority  to  descent 
from  any  single  pair,  but  to  continued  care  in  the  selecting 
and  training  of  many  individuals  during  each  generation. 

Before  discussing  the  three  classes  of  facts,  which  I  have 
selected  as  presenting  the  greatest  amount  of  difliculty  on  the 
theory  of  "  single  centres  of  creation,"  I  must  say  a  few  words 
on  the  means  of  dispersal. 

Means  of  Dlq:)crsaL 

Sir  C  Lyell  and  other  authors  have  ably  treated  this  sub- 
ject. I  can  give  here  only  the  l^riefest  abstract  of  the  more 
important  facts.  Change  of  climate  must  have  had  a  p(jwcr- 
ful  influence  on  migration  ;  an  impassable  region  when  its 
climate  was  different  from  what  it  now  is,  may  have  been  a 
high-road  for  migration;  I  shall,  however,  presently  have  to 
discuss  this  branch  of  the  subject  in  some  detail.  Changes  of 
level  in  the  land  must  also  have  been  highly  influential :  a 
narrow  isthnuis  now  separates  two  marine  faunas ;  submerge 
it,  or  let  it  fonncrly  have  been  submerged,  and  the  two  faunas 


330  MEANS  OF  DISPERS^IL.  Chap.  XI. 

\vill  now  Ijlend  or  may  fonnerly  have  blended  :  where  the  sea 
now  extends,  land  may  at  former  pciiods  have  connected 
islands  or  possibly  even  continents  together,  and  thus  have 
allowed  terrestrial  productions  to  pass  from  one  to  the  other. 
No  geologist  will  dispute  that  great  mutations  of  level  have 
occurred  within  the  period  of  existing  organisms.  Edward 
Forbes  insisted  that  all  the  islands  in  the  Atlantic  must  have 
been  recently  connected  with  Europe  or  Africa,  and  Europe 
likewise  with  America.  Other  authors  have  thus  hj'potheti- 
cally  bridged  over  every  ocean,  and  united  almost  every  island 
to  some  main-land.  If,  indeed,  the  arguments  used  by  Forbes 
are  to  be  trusted,  it  must  be  admitted  that  scarcely  a  single 
island  exists  which  has  not  recently  been  united  to  some  conti- 
nent. This  view  cuts  the  Gordian  knot  of  the  dispersal  of  the 
same  species  to  the  most  distant  points,  and  removes  many  a 
dilhculty :  but,  to  the  best  of  my  judgment,  we  are  not  author- 
ized in  admitting  such  enormous  geograplucal  changes  within 
the  period  of  existing  species.  It  seems  to  me  that  we  have 
abundant  evidence  of  great  oscillations  in  the  level  of  the  land 
or  sea  ;  but  not  of  such  vast  changes  in  the  position  and  exten- 
sion of  our  continents,  as  to  have  imited  them  within  the 
recent  period  to  each  other  and  to  the  several  intervening 
oceanic  islands.  I  freely  admit  the  former  existence  of  many 
islands,  now  buried  beneath  the  sea,  which  may  have  served 
as  halting-places  for  plants  and  for  many  animals  during  their 
migration.  In  the  coral-pi'oducing  oceans  such  sunken  islands 
are  now  marked  by  rings  of  coral  or  atolls  standing  over  them. 
AVhcneverit  is  fully  admitted,  as  no  doubt  it  Avill  some  day  be, 
that  each  species  has  proceeded  from  a  single  birthplace,  and 
Avlien  in  the  course  of  time  we  know  something  definite  about 
the  means  of  distribution,  we  shall  be  enabled  to  speculate  with 
security  on  the  former  extension  of  the  land.  But  I  do  not  be- 
lieve that  it  Avill  ever  be  proved  that  within  the  recent  period 
most  of  our  continents  which  now  stand  quite  separate,  have 
been  continuously,  or  almost  continuously,  united  with  each  oth- 
er, and  Avith  the  many  existing  oceanic  islands.  Several  facts  in 
distribution — such  as  the  great  difference  in  the  marine  faunas 
on  the  opposite  sides  of  almost  every  continent — the  close  re- 
lation of  the  tertiary  inhabitants  of  several  lands  and  even  seas 
to  their  present  inhabitants — the  degree  of  affinity  between 
the  mammals  inhabiting  islands  with  those  of  the  nearest  con- 
tinent, being  in  ])art  determined  (as  we  shall  hereafter  see)  by 
the  depth  of  the  intervening  ocean — these  and  other  such  facts 


CiiAP.  XI.  MEANS  OF  DISPERSAL.  331 

sceni  to  me  oj^poscd  to  tlic  julinissioii  of  such  jirodigious  geo- 
graphical revolutions  -within  the  recent  period,  as  are  necessary 
on  the  view  advanced  b}^  Forbes  and  admitted  by  his  many- 
followers.  The  nature  and  relative  proportions  of  the  inhab- 
itants of  oceanic  islands  likewise  seem  to  me  opposed  to  the 
belief  of  their  former  continuity  with  continents.  Nor  does 
the  almost  universall}'  volcanic  composition  of  such  islands 
iavor  the  admission  that  they  are  the  wrecks  of  sunken  conti- 
nents; if  they  had  originally  existed  as  continental  mountain- 
ranges,  some  at  least  of  the  islands  would  ha^-e  been  formed, 
like  other  mountain-sinnmits,  of  granite,  metamorphic  schists, 
old  fossiliferous  and  other  rocks,  instead  of  consisting  of  mere 
pih.'S  of  volcanic  matter. 

I  nmst  now  say  a  few  words  on  -what  are  called  accidental 
means,  but  which  more  properly  should  be  called  occasional 
means  of  distribution.  1  shall  here  coniine  myself  to  plants.  In 
botanical  works,  this  or  tliat  plant  is  stated  to  be  ill  adapted  for 
-wide  dissemination  ;  but  for  transport  across  the  sea  the  greater 
or  less  facilities  may  be  said  to  be  almost  wholly  unknown. 
Until  I  tried,  -with  JMr.  ]5erkeley's  aid,  a  few  experiments,  it 
-was  not  even  known  how  far  seeds  could  resist  the  injurious 
action  of  sea-water.  To  my  surprise,  I  found  that,  out  of  87 
kinds,  6-4  germinated  after  an  immersion  of  28  days,  and  a  few 
survived  an  inmiersion  of  137  days.  It  deserves  notice  that 
certain  orders  Avere  far  more  injured  than  others :  nine  Legu- 
minoste  were  tried,  and,  with  one  exception,  they  resisted  the 
salt-water  badly ;  seven  species  of  the  allied  orders,  Hydro- 
phjdlaccw  and  Polemoniace:e  were  all  killed  by  a  month's  im- 
mersion. For  convenience'  sake  I  chiefly  tried  small  seeds, 
without  the  cajisule  or  fruit ;  and,  as  all  of  these  sank  in  a  few 
(laj-s,  they  could  not  have  been  floated  across  wide  spaces  of 
th(^  sea,  whether  or  not  they  were  injured  by  the  salt--water. 
Afterward  I  tried  some  larger  fruits,  capsules,  etc.,  and  some 
of  these  floated  for  a  long  time.  It  is  well  kncnvn  what  a  dif- 
ference there  is  in  the  buoyancy  of  green  aiid  seasoned  tim- 
ber; and  it  occurred  to  me  that  floods  might  wash  down  plants 
or  branches,  and  that  these  might  be  dried  on  the  banks,  and 
then  liy  a  fresh  rise  in  the  stream  be  washed  into  the  sea. 
Hence  I  was  led  to  dry  stems  and  branches  of  9-i  ])lants  with 
ripe  fruit,  and  to  plac(;  them  on  sea-water.  The  majority  sank 
quickly,  but  some,  which  while  green  floated  for  a  very  short 
time,  when  drietl  floated  nmch  longer ;  for  instance,  ripe  hazel- 
nuts sank  immediately,  but  when  dried  they  floated  for  90 


332  MEANS   OF  DISPERSAL.  Chap.  XI. 

days,  and  afterward  -wlioii  planted  tliey  cremunatcd ;  an  aspar- 
a2:u.s-j)lant  with  ripe  berries  floated  for  ^3  days,  when  dried  it 
floated  for  85  (lays,  and  the  seeds  afterward  germinated;  the 
ripe  seeds  of  llelosciadimn  sank  in  two  days,  when  dried  they 
floated  for  above  90  days,  and  afterward  germinated.  Alto- 
gether, out  of  the  94  clried  plants,  18  floated  for  above  '28 
days,  and  some  of  the  18  floated  for  a  very  much  longer  period. 
So  that  as  -J;^-  seeds  germinated  after  an  immersion  of  28  days ; 
and  as  1}  ])lants  with  ripe  fruit  (but  not  all  the  same  species 
as  in  the  foregoing  experiment)  floated,  after  being  dried,  for 
above  28  days,  as  far  as  we  may  infer  any  thing  from  these 
scanty  fticts,  we  may  conclude  that  the  seeds  of  ^^  plants  of 
any  country  might  be  floated  by  sea-currents  during  28  days, 
and  would  retain  their  power  of  germination.  In  Johnston's 
Physical  Atlas,  the  average  rate  of  the  several  Atlantic  cur- 
rents is  33  miles  per  diem  (some  currents  running  at  the  rate 
of  GO  miles  per  diem) ;  on  this  average,  the  seeds  of  -jJ^g-  plants 
belonging  to  one  country  might  be  floated  across  924  miles 
of  sea  to  another  country ;  and  when  stranded,  if  blown  to  a 
favorable  spot  by  an  inland  gale,  they  Avould  germinate. 

Subsequently  to  my  experiments,  M.  Martens  tried  similar 
ones,  but  in  a  much  better  manner,  for  he  placed  the  seeds  in 
a  box  in  the  actual  sea,  so  that  they  were  alternately  wet  and 
exposed  to  the  air  like  really  floating  plants.  He  tried  98 
seeds,  mostly  different  from  mine ;  but  he  chose  many  large 
fruits  and  likewise  seeds  from  plants  which  live  near  the  sea; 
and  this  would  have  fiivored  the  average  length  of  their  flota- 
tion and  of  their  resistance  to  the  injurious  action  of  the  salt- 
water. On  the  other  hand,  he  did  not  pre^^iously  dry  the 
plants  or  branches  with  the  fruit ;  and  this,  as  we  have  seen, 
would  have  caused  some  of  them  to  have  floated  much  longer. 
The  result  was,  that  ^  of  his  seeds  floated  for  42  days,  and 
were  then  capable  of  germination.  But  I  do  not  doubt  that 
plants  exposed  to  the  waves  would  float  for  a  less  time  than 
tliose  protected  from  violent  movement  as  in  our  experiments. 
Therefore  it  would  perhaps  be  safer  to  assume  that  the  seeds 
of  about -^/g-  plants  of  a  flora,  after  having  been  dried,  could 
be  floated  across  a  space  of  sea  900  miles  in  Avidth,  and  would 
then  germinate.  The  fact  of  the  larger  fruits  often  floating 
longer  than  the  small,  is  interesting ;  as  plants  with  large 
seeds  or  fruit  could  hardly  be  transported  by  any  other  means  ; 
and  Alph.  do  Candollo  has  shown  that  such  plants  generally 
have  restricted  ranges. 


CiiAP.  XI.  MEANS  OF  DISPERSAL.  833 

But  seeds  111:13'  l)c  occasionally  transported  in  another  man- 
ner. Drift-timber  is  thrown  up  on  most  islands,  even  on  those 
in  the  midst  of  the  widest  oceans;  and  the  natives  of  the 
coral-islands  in  the  Pacific  procure  stones  for  their  tools,  solely 
from  the  roots  of  drifted  trees,  these  stones  being  a  valualjle 
royal  tax.  I  find,  on  examination,  that,  when  irregularly- 
shaped  stones  are  embedded  in  the  roots  of  trees,  small  parcels 
of  earth  are  very  frequently  enclosed  in  their  interstices  and 
behind  them — so  perfectly  that  not  a  particle  could  be  washed 
away  in  the  longest  transport :  out  of  one  small  portion  of. 
earth  thus  completely  enclosed  by  wood  in  an  oak  about  50 
years  old,  three  dicotyledonous  plants  germinated  :  I  am  cer- 
tain of  the  accuracy  of  this  observation.  Again,  I  can  show 
that  the  carcasses  of  birds,  when  floating  on  the  sea,  sometimes 
escape  being  immediately  devoured  ;  and  seeds  of  many  kinds 
in  the  crops  of  floating  birds  long  retain  their  vitality  :  peas 
andvetches,  for  instance,  are  killed  by  even  a  few  days'  immer- 
sion in  sea-water  ;  but  some  taken  out  of  the  crop  of  a  pigeon, 
which  had  floated  on  artificial  salt-water  for  30  days,  to  my 
surprise  nearly  all  germinated. 

LiWng  birds  can  hardly  fail  to  be  highly-effective  agents  in 
the  transportation  of  seeds.  I  could  give  many  facts  showing 
how  frequently  birds  of  many  kinds  are  bloAvn  by  gales  to  vast 
distances  across  the  ocean.  We  may  safely  assume  that  undei" 
such  circumstances  their  rate  of  flight  would  often  be  35  miles 
an  hour ;  and  some  authors  have  given  a  far  higher  estimat'C. 
1  have  never  seen  an  instance  of  nutritious  seeds  passing 
through  the  intestines  of  a  bird ;  but  hard  seeds  of  fruit  pass 
uninjured  through  even  the  digestive  organs  of  a  turkey.  In 
the  ctHirse  of  two  months,  I  picked  up  in  my  garden  12  kinds 
of  seeds,  out  of  the  excrement  of  small  birds,  and  these  seemed 
jierfect,  and  some  of  them,  which  were  tried,  germinated.  But 
the  following  fact  is  more  important :  the  crops  of  birds  do  iif)t 
secrete  gastric  juice,  and  do  not,  as  I  know  by  trial,  injure  in 
the  least  the  germination  of  seeds  ;  now,  after  a  bird  has  found 
and  devoured  a  large  supply  of  food,  it  is  positively  asserted 
that  all  the  grains  do  not  pass  into  the  gizzard  for  twelve  or 
even  eighteen  hours.  A  bird  in  this  interval  might  easily  be 
blown  to  tli<?  distance  of  500  miles,  and  hawks  are  known  to 
look  out  for  tired  birds,  and  the  contents  of  their  torn  crops 
might  thus  readily  get  scattered.  Some  hawks  and  owls  bolt 
their  prey  whole,  and,  after  an  interval  of  from  twelve  to 
twenty  hours,  disgorge  pellets,  which,  as  I  know  from  cxperi- 


S34  MEANS  OF  DISPERSAL.  Cuap.  XI. 

iiicnls  iimdc  in  the  Zoological  Gardens,  include  seeds  capable  of 
genniiiiit  ion.  Some  seeds  of  the  oat,  -wheat,  millet,  canary,  hemp, 
clover,  and  beet,  germinated  after  ha\nng  been  from  twelve  to 
twenty-one  hours  in  the  stomachs  of  different  birds  of  prey; 
and  two  seeds  of  beet  grew  after  having  been  thus  retained 
for  two  d;iys  and  fourteen  hours.  Fresh-water  fisli,  I  find,  eat 
seeds  of  many  land  and  water  plants :  fish  are  frequently  de- 
voured by  birds,  and  thus  the  seeds  might  Ije  transported  fi-om 
place  to  place.  I  forced  many  kinds  of  seeds  into  the  stomachs 
of  dead  fish,  and  then  gave  their  bodies  to  fishing-eagles,  storks, 
and  pelicans  ;  these  birds,  after  an  interval  of  many  hours,  either 
rejected  the  seeds  in  pellets  or  passed  them  in  their  excre- 
ment ;  and  several  of  these  seeds  retained  the  power  of  ger- 
mination. Certain  seeds,  however,  were  always  killed  by  this 
process. 

Locusts  are  sometimes  blown  to  great  distances  from  the 
land;  I  myself  caught  one  370  miles  from  the  coast  of  Africa, 
and  have  heard  of  others  caught  at  greater  distances.  The 
Kev.  R.  T.  Lowe  infonns  Sir  C.  Lyell  that,  in  November,  1844, 
swarms  of  locusts  visited  the  island  of  Madeira.  They  were  in 
countless  numbers,  as  thick  as  the  fiakes  of  snow  in  the  heavi- 
est snow-storm,  and  extended  upward  as  far  as  could  be  seen 
with  a  telescope.  During  two  or  "three  days  they  slowly  ca- 
reered round  in  the  air  in  an  immense  ellipse,  at  least  five  or 
six  miles  in  diameter,  and  at  night  alighted  on  the  taller  trees, 
which  were  completely  coated  with  them.  They  then  disap- 
peared over  the  sea,  as  suddenly  as  they  had  appeared,  and 
have  not  since  visited  the  island.  Now,  in  parts  of  Natal  it  is 
believed  by  some  of  the  farmers,  thougli  on  quite  insufficient 
evidence,  that  injurious  seeds  are  introduced  into  their  grass- 
land in  the  dung  left  by  the  great  fiights  of  locusts  which  often 
visit  that  country.  In  consequence  of  this  belief,  Mr.  Weale 
sent  me  in  a  letter  a  small  jiacket  of  the  dried  pellets,  out  of 
which  I  extracted  imder  the  microscope  several  seeds,  and 
raised  from  them  seven  gi-ass-i)lants,  belonging  to  two  spe- 
cies, in  two  genera.  Hence  a  swarm  of  locusts,  such  as  that 
which  visited  Madeira,  might  readily  be  the  means  of  introdu- 
cing several  kinds  of  plants  into  an  island  lying  far  from  the 
main-land. 

Although  the  beaks  and  fix-t  of  birds  are  generally  clean, 
earth  sometimes  adheres  to  them  :  in  one  easel  removed  sixty- 
one  grains,  and  in  another  case  twenty-two  grains  of  dry  argil- 
laceous earth  from  one   foot  of  a  partridge,  and  in  the  earth 


Chap.  XI.  MEANS  OF  DISPERSAL.  335 

there  was  a  pebble  as  larf^e  as  the  seed  of  a  vetch.  Here  is  a 
better  case  :  the  h\2:  <if  a  woodcock  was  sent  to  mo  by  a  friend, 
with  a  little  cake  of  dry  earth  attached  to  the  sliaiik,  weighini^ 
only  nine  2,rains ;  and  this  contained  a  seed  of  the  toad- 
rush  (Juncus  bufonius)  which  germinated  and  flowered.  Mr. 
Swaysland,  of  Brighton,  who  has  paid  such  close  attention  to 
our  migratory  birds  during  the  last  forty  years,  informs  me  that 
he  has  often  shot  wagtails  (motacilla?)',  wheatears,  and  whin- 
chats  (saxicoloe),  on  their  first  arrival,  before  they  had  alight- 
ed on  our  shores,  and  has  several  times  noticed  little  cakes  of 
earth  on  their  feet.  Many  facts  could  be  given  showing  how 
the  soil  is  almost  everywhere  charged  with  seeds.  For  in- 
stance. Prof.  Newton  sent  me  the  leg  of  a  red-legged  partridge 
(Caccabis  rufa)  which  had  been  wounded  and  could  not  fly, 
with  a  ball  of  hard  earth  adhering  to  it,  and  weighing  six  and 
a  half  ounces.  The  earth  had  been  kept  for  three  years,  but 
•when  broken,  watered,  and  jilaced  under  a  bell  glass,  no  less 
than  82  plants  sprung  from  it:  these  consisted  of  13  monoco- 
tyledons, including  the  common  oat,  and  at  least  one  kind  of 
grass,  and  of  70  dicotyledons,  which  consisted,  judging  from 
tlie  young  leaves,  of  at  least  three  distinct  species.  With  such 
facts  before  us,  can  we  doubt  that  the  many  birds  which  are 
annually  blown  l)y  gales  across  great  spaces  of  ocean,  and  which 
annually  migrate — for  instance,  tlie  millions  of  quails  across 
the  ^Mediterranean — nuist  occasionally  transport  a  few  seeds 
embedded  in  dirt  adiiering  to  their  feet  or  beaks  ?  But  I  shall 
have  to  recur  to  this  subject. 

As  icebergs  are  known  to  be  sometimes  loaded  with  earth 
and  stones,  and  have  even  carried  brushwood,  bones,  and  the 
nest  of  a  land-bird,  it  can  hardly  be  doubted  that  they  must 
occasionally,  as  suggested  by  Lyell,  have  transported  seeds 
from  one  part  to  another  of  the  arctic  and  antarctic  regions ; 
and,  during  the  Glacial  period,  from  one  part  of  the  now  tem- 
Ijcrate  rcgiims  to  another.  In  the  Azores,  from  the  large 
number  of  plants  common  to  Europe,  in  comparis(m  with  the 
species  in  the  otlier  islands  of  thi^  Atlantic,  which  stand  nearer 
to  the  main-land,  and  (as  remarked  by  Mr.  H.  C  Watson)  from 
their  somewhat  northern  character  in  comj^arison  with  the  lati- 
tude, I  suspected  that  th(>S(^  islands  had  been  partly  stocked 
by  ice-borne  seeds,  during  the  Glacial  epoch.  At  my  request 
Sir  C.  Lyell  wrote  to  M.  llartung  to  incjuire  whether  he  had 
observed  erratic  bowlders  on  these  islands,  and  he  answered 
that  lie  had  found  large  fragments  of  granite  and  other  rocks, 


330  MEANS  OF  DISPERSAL.  Chap.  XI. 

■wliicli  do  not  occur  in  the  archipelago.  Hence  we  may  safely 
infer  that  icebergs  formerly  landed  their  rocky  burdens  on  the 
shores  of  these  niid-occau  islands,  and  it  is  at  least  possible 
that  they  may  have  brought  thither  the  seeds  of  northern 
plants. 

Considering  that  tliese  several  means  of  transport,  and  that 
other  means,  which  without  doubt  remain  to  be  discovered, 
have  been  in  action  year  after  year,  for  tens  of  thousands  of 
years,  it  would,  I  think,  be  a  marvellous  fact  if  many  plants  had 
not  thus  become  widely  transported.  These  means  of  trans- 
port are  sometimes  called  accidental,  but  this  is  not  strictly 
correct :  the  currents  of  the  sea  are  not  accidental,  nor  is  the 
direction  of  prevalent  gales  of  wind.  It  should  be  observed 
that  scarcely  any  means  of  transport  would  carry  seeds  for 
very  great  distances;  for  seeds  do  not  retain  their  vitality 
Avhen  exposed  for  a  great  length  of  time  to  the  action  of  sea- 
water;  nor  could  they  be  long  carried  in  the  crops  or  intes-« 
tines  of  birds.  These  means,  however,  would  suffice  for  occa- 
sional transport  across  tracts  of  sea  some  hundred  miles  in 
breadth,  or  from  island  to  island,  or  from  a  continent  to  a 
neighboring  island,  but  not  from  one  distant  continent  to 
another.  The  floras  of  distant  continents  would  not  by  such 
means  become  mingled ;  but  would  remain  as  distinct  as  tliey 
now  are.  The  currents,  from  their  course,  would  never  bring 
seeds  from  North  America  to  Britain,  though  they  might  and 
do  bring  seeds  from  the  West  Indies  to  our  western  shores, 
where,  if  not  killed  by  their  very  long  immersion  in  salt-water, 
they  could  not  endure  our  climate.  Almost  every  year,  one  or 
two  land-birds  are  blown  across  the  whole  Atlantic  Ocean, 
from  North  America  to  the  western  shores  of  Ireland  and 
England  ;  but  seeds  could  be  transported  by  these  rare  wan- 
derers only  by  one  means,  namely,  by  dirt  adhering  to  their 
feet  or  beaks,  which  is  in  itself  a  rare  accident.  Even  in  this 
case,  how  small  the  chance  would  be  of  a  seed  falling  on  fa- 
vorable soil,  and  coming  to  matuiity !  But  it  would  be  a  great 
error  to  argue  that  because  a  well-stocked  island,  like  Great 
Britain,  has  not,  as  far  as  is  known  (and  it  would  be  very  diffi- 
cult to  prove  this),  received  within  the  last  few  centuries, 
through  occasional  means  of  transport,  immigrants  from  Eu- 
lope  or  any  other  continent,  that  a  poorly-storked  island, 
though  standing  more  remote  from  the  main-land,  would  not 
receive  colonists  by  similar  means.  Out  of  a  hundred  seeds 
or   animals  transported   to  an  island,  even  if   far  less  well 


CnxF.  XI.     DISPERSAL  DURING  THE  GLACTAL  PERIOD.  337 

stocked  than  Britain,  perhaps  not  more  than  one  would  be  so 
well  litted  to  its  new  home  as  to  become  naturalized.  But 
this,  as  it  seems  to  me,  is  no  valid  arf^ument  against  "what 
would  be  effected  by  occasional  means  of  transport,  during  tlu; 
long  lapse  of  geological  time,  while  the  island  was  being  up- 
heaved, and  before  it  had  become  fully  stocked  with  inhabit- 
ants. On  almost  bare  land,  with  few  or  no  destructive  insects 
or  birds  living  there,  nearly  every  seed  which  chanced  to  arrive, 
if  fitted  for  the  climate,  would  germinate  and  survive, 

Disjyersal  durbuj  the  Glacial  Period. 

The  identity  of  many  plants  and  animals,  on  mountain- 
gunnnits,  separated  from  each  other  by  hundreds  of  miles  of 
lowlands,  where  Alpine  species  could  not  possibly  exist,  is  one 
of  llie  most  striking  cases  known  of  the  same  species  living  at 
distant  points,  without  the  apparent  possibility  of  their  having 
migrated  from  one  point  to  the  other.  It  is  indeed  a  remark- 
able fact  to  see  so  many  plants  of  the  same  species  living  on 
the  snowy  regions  of  the  Alps  or  Pyrenees,  and  in  the  extreme 
jiorthern  parts  of  Europe ;  but  it  is  far  more  remarkable  that 
the  plants  on  the  White  Mountains,  in  the  United  States  of 
America,  arc  all  the  same  with  those  of  Labrador,  and  nearly 
all  the  sanie,  as  we  hear  from  Asa  Gray,  with  those  on  the 
loftiest  mountains  of  Europe.  Even  as  long  ago  as  1747,  such 
facts  led  Gmelin  to  conclude  that  the  same  species  must  have 
Ijcen  independently  created  at  several  distinct  points ;  and  we 
might  have  remained  in  this  same  belief,  had  not  Agassiz  and 
others  called  vivid  attention  to  the  Glacial  period,  which,  as 
we  shall  immediately  see,  affords  a  simple  exfjlanation  of  these 
facts.  We  have  evidence  of  almost  every  conceivable  kind, 
organic  and  inorganic,  that,  within  a  very  recent  geological 
jx'riod,  central  Em-ope  and  North  America  suffered  under  an 
arctic  climate.  The  ruins  of  a  house  burnt  by  lire  do  not  tell 
their  tale  moni  plainly  than  do  the  mountains  of  Scotland  and 
Wales,  with  their  scored  flanks,  polishi^d  surfaces,  and  perched 
bowlders,  of  the  icy  streams  with  which  their  valleys  W(M-e  late- 
Iv  filled.  So  grcatlv  has  the  climate  of  Europe  clianged,  thai, 
in  Northern  Jtalv,  gigantic  moraines,  left  bv  old  glaciers,  are 
now  clothed  by  tlie  vine  and  maize,  'J'hroughout  a  larg(^  part 
of  the  United  States,  erratic  bowlders  and  scored  rocks  ])jainly 
reveal  a  former  cold  j)eriod, 

Tlie  former  influence  of  the  glacial  climate  on  the  distribu- 
15 


338  DISPERSAL  Cuat,  Xi. 

lion  of  the  inliabitiints  of  Europe,  as  cxj)lained  hy  Edward 
Forbes,  is  substantially  as  follows.  But  we  shall  follow  the 
changes  more  readil}',  by  supposing  a  new  glacial  period  slowly 
to  come  on,  and  then  pass  away,  as  formerly  occurred.  As  the 
cold  came  on,  and  as  each  more  southern  zone  became  fitted 
for  the  inhabitants  of  the  north,  they  would  take  the  places  of 
the  former  inhabitants  of  the  temperate  regions.  The  latter, 
at  the  same  time,  would  travel  farther  and  farther  southward, 
unless  thoy  were  stopped  by  bairiers,  in  which  case  they  would 
perish.  The  mountains  would  become  covered  with  snow  and 
ice,  and  their  former  Alpine  inhabitants  would  descend  to  the 
plains.  By  the  time  that  the  cold  had  reached  its  maximum, 
we  should  have  an  arctic  fauna  and  flora,  covering  the  central 
parts  of  Europe,  as  far  south  as  the  Alps  and  Pyrenees,  and 
even  stretching  into  Spain.  The  now  temperate  regions  of  the 
United  States  would  likewise  be  covered  by  arctic  plants  and 
animals,  and  these  would  be  nearly  the  same  with  those  of 
Europe  ;  for  the  present  cireumpolar  inhabitants,  which  we  sup- 
pose to  have  everywhere  travelled  southward,  are  remarkably 
uniform  round  the  world. 

As  the  warmth  returned,  the  arctic  forms  would  retreat 
northward,  closely  followed  up  in  their  retreat  by  the  produc- 
tions of  the  more  temperate  regions.  And  as  the  snow  melted 
from  the  bases  of  the  mountains,  the  arctic  forms  Avould  seize 
on  the  cleared  and  thawed  ground,  always  ascending,  as  the 
warmth  increased  and  the  snow  still  further  disappeared,  higher 
and  higher,  while  their  brethren  were  pursuing  their  northern 
journey.  Hence,  when  the  warmth  had  fully  returned,  the 
same  species,  which  had  lately  lived  together  in  a  body  on  the 
European  and  North  American  lowlands,  Avould  again  be  found 
in  the  arctic  regions  of  the  Old  and  New  Worlds,  and  on  many 
isolated  mountain-summits  far  distant  from  each  other. 

Thus  we  can  understalid  the  identity  of  many  plants  at 
points  so  immensely  remote  as  on  the  mountains  of  the  United 
States  and  of  Europe.  We  can  thus  also  understand  the  fact 
that  the  Alpine  plants  of  each  mountain-range  are  more  espe- 
cially related  to  the  arctic  forms  living  due  north  or  nearly  due 
north  of  them  :  for  the  first  migration  when  the  cold  came  on, 
and  the  remigration  on  the  returning  warmth,  would  generally 
have  been  due  south  and  north.  The  Alpine  plants,  for  exam- 
ple, of  Scotland,  as  remarked  by  Mr.  II.  C.  Watson,  and  those 
of  the  Pyrenees,  as  remarked  by  Ramond,  are  more  especially 
allied  to  the  plants  of  northern   Scandinavia ;    those  of  the 


CiiAi'.  XI.  DUKING   THE   GLACIAL  PERIOD.  339 

United  States  to  Labrador ;  those  of  the  mountains  of  Siberia 
to  the  arctic  regions  of  that  country.  These  views,  f^rounded 
as  they  are  011  the  perfectly  well-ascertained  occurrence  of  a 
former  Glacial  period,  seem  to  me  to  explain  in  so  satisfactory 
a  manner  the  present  distribution  of  the  Alpine  and  arctic  pro- 
ductions of  Europe  and  .Vmcrica,  that,  when  in  other  regions 
we  lind  the  same  species  on  distant  mountain-summits,  Ave  may 
almost  conclude,  without  other  evidence,  that  a  colder  climate 
lV)rnierly  permitted  their  migration  across  the  intervening  low- 
lands, now  become  too  warm  for  their  existence. 

As  the  arctic  forms  moved  first  southward  and  afterward 
backward  to  the  north,  in  unison  with  the  changing  climate, 
they  w  ill  not  have  been  exposed  during  their  long  migrations 
to  any  great  diversity  of  temperature ;  and,  as  they  all  migrated 
in  a  body  tog-ether,  their  mutual  relations  will  not  have  been 
much  disturlicd.  Hence,  in  accordance  with  the  principles  in- 
culcated in  tliis  volume,  these  forms  will  not  have  been  liabli> 
to  much  modification.  But  with  the  Alpine  productions,  left 
isolated  fi-om  the  moment  of  the  returning  warmth,  first  at  the 
bases  and  ultimately  on  the  summits  of  the  mountains,  the  case 
will  have  been  somewhat  different;  for  it  is  not  likely  that  all 
the  same  arctic  species  will  have  been  left  on  mountain-ranges 
far  distant  from  each  other,  antl  have  survived  there  ever  since; 
they  will,  also,  in  all  probability,  have  become  mingled  Avitli 
ancient  Alpine  species,  which  must  have  existed  on  the  moun- 
tains before  tlie  commencement  of  the  Glacial  epoch,  and  which 
during  its  coldest  ])eriod  will  have  been  temporarily  driven 
down  to  the  plains  ;  they  will,  also,  have  been  exposed  to  some- 
what different  climatal  influences.  Their  mutual  relations  will 
thus  have  been  in  some  degree  disturbed  ;  consequiMitlv  they 
will  have  been  liable  to  modification  ;  and  this  we  find  has  been 
the  case  :  for  if  we  compare  the  present  Alpine  j)lants  and  ani- 
mals of  the  several  great  European  mountain-ranges  one  with 
another,  though  many  of  the  species  remain  idmitically  the  same, 
some  exist  as  varieties,  some  as  doubtful  forms  or  sub-species, 
and  some  as  certainly  distinct  yet  closely-allied  species  repre- 
senting each  other  on  the  several  ranges. 

In  the  foregoing  illustration  T  have  assumed  that  at  the 
commencement  of  our  imagin.ary  Glacial  period,  the  arctic  pro- 
ductions were  as  uniform  round  the  polar  regions  as  they  arc 
at  the  present  day.  But  it  is  necessary  also  to  include  many 
sulvarctic  and  some  few  temperate  forms,  for  some  of  these  are 
the  same  on  the  lower  mountain-slopes  and  on  the  plains  of 


340  DISPERSAL  Chaj-.  XI. 

North  America  and  Europe  ;  and  it  may  be  asked  how  I  ac- 
count for  tliis  degree  of  uniformity  in  the  sub-arctic  and  temper- 
ate forms  round  tlie  world,  at  the  commencement  of  the  real 
Glacial  period.  At  the  present  day,  the  sub-arctic  and  northern 
temperate  productions  of  the  Old  and  New  Worlds  are  sepa- 
rated from  each  other  by  the  whole  Atlantic  Ocean  and  by  the 
nortliern  part  of  the  Pacific.  During  the  Glacial  period,  when 
the  inhabitants  of  the  Old  and  New  Worlds  lived  farther  south- 
ward than  they  do  at  present,  they  must  have  been  still  more 
completely  separated  from  each  other  by  wider  spaces  of  ocean ; 
so  that  it  may  well  be  asked  how  the  same  species  could  have 
entered  the  two  continents  then  so  widely  separated.  The  ex- 
planation, I  believe,  lies  in  the  nature  of  the  climate  before  the 
commencement  of  the  Glacial  period.  At  this,  the  newer  Plio- 
cene period,  the  majority  of  the  inhabitants  of  the  world  were 
specifically  the  same  as  now,  and  we  have  good  reason  to 
believe  that  the  climate  was  warmer  than  at  the  present  day. 
Hence  we  may  suppose  that  the  organisms  which  now  live  un- 
der latitude  60°,  lived  during  the  Pliocene  jieriod  farther  north 
under  the  Polar  Circle,  in  latitude  CG°-G(°  ;  and  that  the  pres- 
ent arctic  productions  then  lived  on  the  broken  land  still  nearer 
to  the  pole.  Now,  if  we  look  at  a  terrestrial  globe,  we  see  un- 
der the  Polar  Circle  that  there  is  almost  continuous  land  from 
western  Europe,  through  Siberia,  to  eastern  America.  And 
this  ccHitinuity  of  the  circumpolar  land,  with  the  consequent 
freedom  imder  a  more  favorable  climate  for  intermigration,  will 
account  for  the  supposed  uniformity  of  the  sub-arctic  and  tem- 
perate productions  of  the  Old  and  New  Worlds,  at  a  period 
anterior  to  the  Glacial  epoch. 

Believing,  from  reasons  before  alluded  to,  that  our  conti- 
nents have  long  remained  in  nearly  the  same  relative  position, 
though  sul)jected  to  large  but  partial  oscillations  of  level,  I 
am  strongly  inclined  to  extend  the  above  view,  and  to  infer 
that  during  some  still  earlier  and  still  vrarmer  period,  such  as 
the  older  Pliocene  period,  a  large  number  of  the  same  plants 
and  animals  inhabited  the  almost  continuous  circumpolar  land  ; 
and  that  these  plants  and  animals,  both  in  the  Old  and  New 
Worlds,  began  slowly  to  migrate  southward  as  the  climate  be- 
came less  warm,  long  before  the  commencement  of  the  Glacial 
period.  We  now  see,  as  I  believe,  their  descendants,  mostly 
in  a  modified  condition,  in  the  central  parts  of  Europe  and  the 
United  States.  ( )n  this  A-iew  we  can  understand  tlie  relation- 
shi]),   ^^itll  very  little  identity,  l)etween  the    productions  of 


Chap.  XI.  DURING  TIIP:  GLACIAL  PEKIOD.  34I 

North  America  and  Europe — a  relationship  whicli  is  highly 
romarkai)lc,  considering  the  distance  of  the  two  areas,  and 
tlieir  separation  hy  tlie  whole  Atlantic  Ocean.  We  can  fur- 
ther understand  the  singular  fact  remarked  on  by  several 
observers,  that  the  productions  of  Europe  and  America  during 
the  later  tertiary  stages  -were  more  closely  related  to  each 
other  than  they  are  at  the  present  time ;  for  during  tliese 
warmer  periods  the  northern  parts  of  the  Old  and  New  Worlds 
will  have  been  almost  conthiuously  united  by  land,  serving  as 
a  bridge,  since  rendered  impassable  by  cold,  for  the  intermi- 
gration  of  their  inhabitants. 

During  the  slowly-decreasing  warmth  of  the  Pliocene  pe- 
riod, as  soon  as  the  species  in  common,  which  inliabitcd  the 
New  and  0!d  Worlds,  migrated  south  of  the  Polar  Circle,  they 
would  be  completely  cut  off  from  each  other.  This  separation, 
as  -far  as  the  more  temperate  productions  are  concerned,  must 
have  taken  place  long  ages  ago.  As  the  plants  and  animals 
migrated  southward,  they  would  become  mingled  in  the  one 
great  region  with  the  native  American  productions,  and  would 
have  had  to  compete  with  them  ;  and,  in  the  other  great  region, 
with  those  of  the  Old  World.  Consequently  we  have  here 
every  tiling  favorable  for  much  modification  —  for  far  more 
modification  than  with  the  Alpine  productions,  left  isolated, 
within  a  much  more  recent  period,  on  tlie  several  mountain- 
ranges  and  on  the  arctic  lands  of  Europe  and  North  America. 
Hence  it  has  come  that,  when  we  compare  the  now  living  pro- 
ductions of  the  temperate  regions  of  the  New  and  Old  Worlds, 
we  find  very  few  identical  species  (though  Asa  Gray  has  late- 
ly shown  that  more  plants  are  identical  than  was  formerly  sup- 
j)Osed),  but  we  find  in  every  great  class  many  forms,  which 
some  naturalists  rank  as  geographical  races,  and  others  as  dis- 
tinct species ;  and  a  host  of  closely-allied  or  representative 
forms  which  are  ranked  by  all  naturalists  as  specifically  dis- 
tinct. 

As  on  the  land,  so  in  the  waters  of  the  sea,  a  slow  southern 
migration  of  a  marine  fauna,  which,  during  the  Pliocene  or 
even  a  somewhat  earlier  pcried,  was  nearly  imiform  along  the 
continuous  shores  of  tlie  Pohir  Circle,  will  account,  on  tlie  the- 
ory of  modification,  for  many  closely-allied  forms  now  living 
in  marine  areas  completely  sundered.  Thus,  I  tliink,  we  can 
imderstand  the  ])resence  of  some  still  existing  and  of  some  ter- 
tiary closely-allied  fijrms  on  the  eastern  anti  western  shores  of 
temperate  North  America ;  and  the  still  more  striking  fact  of 


342  alti:i:nate  glacial  tliuods  chap.  xl 

many  clost'ly-allicd  crustaceans  (as  described  in  Dana's  admir- 
able work),  of  some  fish  and  other  marine  animals,  in  the  Med- 
iterranean and  in  the  seas  of  Japan — these  two  areas  being 
now  completely  separated  by  the  breadth  of  a  whole  continent 
and  by  a  wide  space  of  ocean. 

These  cases  of  close  relationship  in  species  either  now  or 
formerly  inhabiting  the  seas  on  the  eastern  and  western  shores 
of  North  America,  the  Mediterranean,  and  Japan,  and  the  tem- 
perate lands  of  North  America  and  Europe,  are  inexplicable 
on  the  theory  of  creation.  AVc  cannot  maintain  that  such  spe- 
cies have  been  created  alike,  in  correspondence  with  the  neai'- 
ly  similar  physical  conditions  of  the  areas  ;  for  if  we  compare, 
for  instance,  certain  parts  of  South  America  with  j^arts  of 
South  Africa  or  Australia,  Ave  see  countries  closely  similar  in 
all  their  j^hysical  conditions,  hut  with  inhabitants  utterly  dis- 
similar. 

Alternate  Glacial  Periods  of  the  Korth  and  South. 

But  we  must  return  to  our  more  immediate  subject.  I  am 
convinced  that  Forbes's  view  may  be  largely  extended.  In 
Europe  we  meet  with  the  plainest  evidence  of  the  Glacial  pe- 
riod, from  the  Avcstcrn  shores  of  Britain  to  the  Ural  range,  and 
southward  to  the  Pyrenees.  We  may  infer,  from  the  frozen 
mammals  and  nature  of  the  mountain  vegetation,  that  Siberia 
was  similarly  aflected.  In  the  Lebanon,  according  to  Dr. 
Hooker,  perpetual  snow  formerly  covered  the  central  axis,  and 
fed  glaciers  which  rolled  4,000  feet  down  its  valleys.  Along 
the  Himalaya,  at  points  900  miles  apart,  glaciers  have  left  the 
marks  of  their  former  low  descent ;  and,  in  Sikkim,  Dr.  Hooker 
saw  maize  growing  on  gigantic  ancient  moraines.  Southward 
of  the  Asiatic  Continent,  on  the  opposite  side  of  the  equator, 
we  now  know,  from  the  excellent  researches  of  Dr.  J.  Haast 
and  Dr.  Hector,  that  immense  glaciers  formerly  descended  to 
a  low  level  in  New  Zealand ;  and  the  same  plants  foimd  by 
Dr.  Hooker  on  wideh'-separated  mountains  in  this  island  tell 
the  same  story  of  a  former  cold  period.  From  facts  commimi- 
catcd  to  me  by  tlie  Rev.  W.  B.  Clarke,  it  appears  also  that 
there  are  traces  of  former  glacial  action  on  the  mountains  of 
the  southeastern  corner  of  Australia. 

Looking  to  America:  in  the  northern  half,  ice-born  frag- 
ments of  rock  have  been  observed  on  the  eastern  side  of  the 
oontinent,  as  far  south  as  kit.  3G°-37°,  and  on  the  shores  of  the 


Cjur.  XI.  OF  THE  NORTH  AND  SOUTH.  343 

Pncific,  where  tlic  climate  is  now  so  difiercnt,  as  far  south  as 
lat  4G''.  Erratic  bowlders  have,  also,  been  noticed  on  the 
Rocky  Mountains.  In  the  Cordillera  of  South  America,  nearly 
under  the  equator,  glaciers  once  extended  far  Ix'low  their  pres- 
ent level.  In  central  Chili  I  examined  a  vast  mound  of  detri- 
tus with  grciit  bowlders,  crossing  the  Portillo  valle}',  which 
there  can  hardly  be  a  doubt  once  formed  a  huge  moraine ;  and 
Mr.  D.  Forbes  informs  me  that  he  found  in  various  parts  of  the 
Cordillera,  from  lat,  13°  to  30°  S.,  at  about  the  height  of 
12,000  feet,  deeply-furrowed  rocks,  resembling  those  with 
which  he  was  familiar  in  Norway,  and  likewise  great  masses 
of  detritus,  including  grooved  pebbles.  Along  this  whole 
space  of  the  Cordillera  true  glaciers  do  not  now  exist  even  at 
nmcli  more  considerable  heights.  Farther  south  on  both  sides 
of  the  continent,  from  lat.  41°  to  the  southernmost  extremity, 
we  have  the  clearest  evidence  of  former  glacial  action,  in  nu- 
merous immense  bowlders  transported  far  from  their  parent 
source. 

From  these  several  facts,  namely,  from  the  glacial  action 
having  extended  all  round  the  northern  and  southern  hemis- 
pheres— from  tlic  period  having  been  in  a  geological  sense  re- 
cent in  both  hemispheres — from  its  having  lasted  in  both  dur- 
ing a  great  length  of  time,  as  may  be  inferred  from  the  amount 
of  work  effected — and  lastly  from  glaciers  having  recently  de- 
scended to  a  low  level  along  the  whole  line  of  the  Cordillera,  it 
formerly  appeared  to  me  that  we  could  not  avoid  the  conclusion 
that  the  temperature  of  the  whole  world  had  been  simultane- 
ously lowered  during  the  Glacial  period.  But  now  Mr.  CroU, 
in  a  series  of  admirable  memoirs,  lias  attempted  to  show  that 
a  glacial  condition  of  climate  is  the  result  of  various  physical 
causes,  brought  into  operation  by  an  increase  in  the  eccentricity 
of  the  earth's  orlnt.  All  these  causes  tend  toward  the  same 
end ;  but  the  most  powerful  appears  to  be  the  influence  of  the 
oocentricity  of  the  orbit  upon  oceanic  ciuTcnts.  It  follows,  from 
Mr.  Croll's  researches,  that  cold  periods  regularly  recur  every 
ten  or  fifteen  thousand  years;  but  that  at  much  longer  inter- 
vals the  cold,  owing  to  certain  contingencies,  is  extremely  se- 
vere, and  lasts  for  a  great  length  of  time.  Mr.  Cn)ll  believes 
that  the  last  great  Glacial  period  occurred  about  2-40,000  years 
ago,  and  endured  with  slight  alterations  of  climate  for  about 
160,000  years.  With  respect  to  more  ancient  Glacial  periods, 
several  geologists  arc  convinced  from  direct  evidence  that  such 
occurred  during  the  Miocene  and   Eocene  fonnations,  not  to 


"344  ALTERNATE  GLACIAL  TEKIODS  Chap.  XI. 

mention  still  more  ancient  formations.  But  in  relation  to  our 
present  subject,  the  most  important  result  arrived  at  by  Mr, 
Croll  is,  that  whenever  the  northern  hemisphere  passes  through 
a  cold  period,  the  temperature  of  the  southern  hemisphere  is 
actually  raisctl,  with  the  winters  rendered  much  milder,  chiefly 
through  changes  in  the  direction  of  the  ocean-currents.  So, 
conversely,  it  is  with  the  northern  hemisphere,  when  the  south- 
ern passes  through  a  glacial  period.  These  conclusions  have, 
as  we  shall  immediately  see,  a  most  important  bearing  on  geo- 
graphical distribution ;  but  I  will  first  give  the  facts  which  de- 
mand an  explanation. 

In  South  America,  Dr.  Hooker  has  shown  that,  besides  many 
closely-allied  species,  between  forty  and  fifty  of  the  flowering 
plants  of  Terra  del  Fuego,  forming  no  inconsiderable  part  of 
its  scanty  flora,  are  common  to  North  America  and  Europe, 
enormously  remote  as  these  areas  in  opposite  hemispheres  are 
from  each  other.  On  the  lofty  mountains  of  equatorial  America 
a  host  of  peculiar  species  belonging  to  European  genera  occur. 
On  the  Organ  Mountains  of  Brazil,  some  few  temperate  Euro- 
pean, some  Antarctic,  and  some  Andean  genera  were  found 
by  Gardner,  which  do  not  exist  in  the  low  intervening  hot 
countries.  On  the  Silla  of  Caraccas  the  illustrious  Humboldt 
long  ago  found  species  belonging  to  genera  characteristic  of 
the  Cordillera. 

In  Africa,  several  forms  characteristic  of  Europe  and  some 
few  representatives  of  the  flora  of  the  Cape  of  Good  Hope  oc- 
cur on  the  Mountains  of  Abj'ssinia.  At  the  Cape  of  Good 
Hope  a  very  few  European  species,  believed  not  to  have  been 
introduced  by  man,  and  on  the  mountains  several  representa- 
tive European  forms  are  found,  which  have  not  been  discovered 
in  the  intertrojDical  parts  of  Africa.  Dr.  Hooker  has  also  lately 
shown  that  several  of  the  plants  living  on  the  upper  parts  of 
the  lofty  island  of  Fernando  Po  and  on  the  neighboring  Cam- 
eroon Mountains,  in  the  Gulf  of  Guinea,  are  closely  related  to 
those  on  the  Mountains  of  Abyssinia,  and  likewise  to  those  of 
Icinperate  P^urope.  It  now  also  appears,  as  I  hear  froni  Dr. 
Hooker,  tliat  some  of  these  same  temperate  plants  have  been 
discovered  by  the  R;'v.  R.  T.  Lowe  on  the  mountains  of  the 
Cape  de  V^erde  Islands.  This  extension  of  the  same  temperate 
forms,  almost  under  the  equator,  across  the  whole  continent  of 
Africa  and  to  the  mountains  of  the  Cape  de  Verde  archipelago, 
is  one  of  the  most  astonishing  facts  ever  recorded  in  the  dis' 
tribution  of  plants. 


CnAP.  XI.  OF  THE  NORTH  AND  SOUTH.  345 

On  the  Himalaya,  and  on  the  isolated  mountain-ranges  of 
the  Peninsula  of  India,  on  the  heights  of  Cejlon,  and  on  the 
volcanic  cones  of  Java,  many  plants  occur,  cither  identicall}'  the 
same  or  representing  each  other,  and  at  the  same  time  repre- 
senting plants  of  Europe,  not  found  in  the  intervening  hot  low- 
lands. A  list  of  the  genera  of  plants  collected  on  the  loftier 
peaks  of  Java  raises  a  picture  of  a  collection  made  on  a  hillock 
in  Europe  !  Still  more  striking  is  the  fact  that  pecidiar  south- 
ern Australian  forms  are  represented  by  certain  j)lants  grow- 
ing on  the  summits  of  the  mountains  of  Borneo.  Some  of  these 
Australian  forms,  as  I  hear  from  Dr.  Hooker,  extend  along  the 
heights  of  the  peninsula  of  Malacca,  and  are  thinly  scattered  on 
the  one  hand  over  India,  and  on  the  other  hand  as  far  nortli  as 
Japan. 

On  the  southern  mountains  of  Australia,  Dr.  F.  Muller  has 
discovered  several  European  species ;  other  species,  not  intro- 
duced by  man,  occur  on  the  lowlands;  and  a  long  list  can  be 
given,  as  I  am  informed  by  Dr.  Hooker,  of  European  genera, 
found  in  Australia,  but  not  in  the  intermediate  torrid  regions. 
In  the  admirable  "  Introduction  to  the  Flora  of  New  Zealand," 
by  Dr.  Hooker,  analogous  and  strilving  facts  are  given  in  re- 
gard to  the  ])lants  of  that  large  island.  Hence  we  see  that 
certain  plants  growing  on  the  more  lofty  mountains  of  the 
tropics  in  all  parts  of  the  world,  and  on  the  temperate  plains  of 
the  north  and  south,  are  either  the  same  identical  species  or 
varieties  of  the  same  species.  It  should,  however,  be  observed 
that  these  plants  are  not  strictly  Arctic  forms ;  for,  as  Mr.  H. 
V.  Watson  has  remarked,  "  in  receding  from  polar  toward 
equatorial  latitudes,  the  Alpine  or  mountain  floras  really  be- 
come less  and  less  Arctic."  Besides  these  identical  and  closely- 
allied  forms,  many  species  inhabiting  the  same  widely-sundered 
areas  behjng  to  genera  not  now  found  in  the  intermediate  trop- 
ical lowlands. 

These  brief  remarks  a]iply  to  plants  alone ;  but  some  few 
analogous  facts  could  be  givi'U  in  regard  to  terrestrial  animals. 
In  marine  productions,  similar  cases  likewise  occur;  as  an  ex- 
ample, I  may  quote  a  statement  by  the  highest  authority,  Prof. 
Dana,  that  ''it  is  certainly  a  wonderful  fact  that  New  Zealand 
should  have  a  closer  reseml)lanc«;  in  its  Crustacea  to  Great 
Ijiitain,  its  anlijiode,  than  to  anv  otiier  part  of  the  world." 
Sir  J.  Kiclianlson,  also,  speaks  of  the  reappearance  on  the 
shores  of  New  Zealand,  Tasnianiii,  etc.,  of  northern  forms  of 
fish.     Dr.  Hooker  informs  me  that  twenty-five  species  of  Algaj 


346  ALTERNATE   GLACIAL  I'EKIODS  CirAr.  XI. 

arc  common  to  Ncn'  Zealand  and  to  Europe,  Inti  Iiave  not  beer 
found  in  the  inlennediate  tropical  seas. 

From  the  foregoing^  facts,  namely,  the  presence  of  temperate 
forms  on  the  highlands  across  the  whole  of  equatorial  iVfrica, 
and  along  the  Peninsula  of  India  to  Ceylon  and  the  Malay  archi- 
pelago, and  in  a  less  ■\vell-raarked  mann(T  across  the  wide  ex- 
panse of  tropical  South  America,  it  appears  almost  certain  that 
at  some  former  period,  no  doubt  during  the  most  severe  part 
of  the  Glacial  period,  the  lowlands  of  these  great  continents 
were  everyAvhere  tenanted  under  the  equator  by  a  considerable 
number  of  temperate  forms.  At  tliis  ])criod  the  equatorial  cli- 
mate at  the  level  of  the  sea  was  probably  about  the  same  with 
that  now^  experienced  at  the  height  of  from  five  to  six  thousand 
feet  vmder  the  same  latitudes,  or  perhaps  even  rather  cooler. 
During  this,  the  coldest  period,  the  lowlands  under  the  equator 
must  have  been  clothed  with  a  mingled  tropical  and  temperate 
vegetation,  like  that  described  by  Hooker  as  growing  luxuri- 
antly at  the  height  of  from  four  to  five  thousand  feet  on  the 
lower  slopes  of  the  Himalaya,  but  with  perhaps  a  still  greater 
preponderance  of  temperate  forms.  So,  again,  on  the  moun- 
tainous island  of  Fernando  Po,  in  the  Gulf  of  Guinea,  Mr.  Mann 
found  temperate  European  forms  beginning  to  appear  at  the 
height  of  about  five  thousand  feet.  On  the  mountains  of 
Panama,  at  the  height  of  only  two  thousand  feet.  Dr.  Seemann 
found  the  vegetation  like  that  of  Mexico,  "  Avith  forms  of  the 
torrid  zone  harmoniously  blended  with  those  of  the  temperate." 

Now  let  us  see  Avhether  Mr.  Croll's  conclusion,  that  Avhen 
the  northern  hemisphere  sufTcred  fi-om  the  extreme  cold  of  the 
great  Glacial  period,  the  southern  hemisphere  Avas  actually 
Avarmer,  throAvs  any  clear  light  on  the  present  apparently  inex- 
])licable  distribution  of  A^arious  organisms  in  the  temperate 
jiarts  of  both  hemispheres,  and  on  mountains  of  the  tropics. 
The  Glacial  period  as  measured  by  ^-ears,  7uust  have  been  very 
long;  and,  Avhcn  avc  remember  OA'cr  Avhat  vast  spaces  some 
naturalized  plants  and  animals  have  spread  Avithin  a  fcAV  cen- 
turies, this  period  Avill  haAC  been  ample  for  any  amoimt  of  mi- 
gration. As  the  cold  became  more  and  more  intense,  Ave  knoAV 
that  Arctic  forms  iuA'aded  the  temperate  regions  ;  and,  from  the 
facts  just  given,  there  can  hardly  be  a  doubt  that  some  of  the 
more  A'igorous,  dominant,  and  widest-spreading  temperate  forms 
actually  then  iuA'aded  the  equatorial  loAvlands.  The  inhabitants 
of  these  lowlands  Avould  at  the  same  time  migrate  to  the  tropi- 
Ciil  and  sub-tropical  regions  of  the  south,  for  the  southern  hemi- 


CiiAr.  XI.  OF  THE  NOKTII  AND  SOUTH.  347 

splicre  was  at  this  period  warmer.  On  the  decline  of  the  Ghi- 
cial  ]>eriod,  as  both  liemis])heres  gradually  recovered  their 
former  temperatures,  the  northern  temperate  forms,  livins;  on 
the  lowlands  under  tlie  equator,  would  be  driven  to  their  former 
homes  or  be  destroyed,  being  replaced  by  the  equatorial  forms 
returning  from  the  south.  Some,  howeveK,  of  the  northern 
temperate  forms  would  almost  certainly  ascend  any  adjoining 
highland,  where,  if  sufficiently  lofty,  they  would  long  survive, 
like  the  Arctic  forms  on  the  mountains  of  Europe.  They  might 
survive,  even  if  the  climate  was  not  perfectly  fitted  for  them, 
for  the  change  of  temperature  must  have  been  very  slow,  and 
plants  undoubtedly  possess  a  certain  capacity  for  acclimatiza- 
tion, as  slio\\Ti  by  their  transmitting  to  their  offspring  different 
constitutional  powers  of  resisting  heat  and  cold. 

In  the  regular  course  of  events  the  southern  hemisphere 
would  be  subjected  to  a  severe  Glacial  period,  with  the  northern 
hemisphere  rendered  warmer  ;  and  then  the  southern  temperate 
forms  would  in  their  turn  invade  the  equatorial  lowlands.  The 
northern  forms  which  had  before  been  left  on  the  mountains 
would  now  descend  and  mingle  Avith  the  southern  forms. 
These  latter,  Avhen  the  warmth  returned,  Avould  return  to  their 
former  homes,  leaving  some  few  species  on  the  mountains,  and 
carrying  southward  with  them  some  of  the  northern  temper- 
ate forms  which  had  descended  from  their  mountain  fastnesses. 
Thus,  we  should  have  some  few  species  identically  the  same  in 
the  northern  and  southern  temperate  zones  and  on  the  moun- 
tains of  the  intermediate  tropical  regions.  But  the  species  left 
during  a  long  time  on  these  mountains,  or  in  opposite  hemi- 
spheres, would  have  to  compete  Avith  many  new  forms,  and 
would  be  exposed  to  somewhat  clifTerent  physical  conditions  ; 
hence  tlicy  would  be  eminently  lialjle  to  modification,  and 
would  generally  now  exist  as  varieties  or  as  representative  s]>c- 
cies ;  and  this  is  the  case.  We  must,  also,  bear  in  mind  the 
occurrence  in  both  hemispheres  of  former  Glacial  jieriods ;  for 
these  will  account,  in  accordance  with  the  same  principles,  for 
the  many  quite  distinct  species  inhabiting  the  same  widely- 
separated  areas,  and  belonging  to  genera  not  now  found  in  the 
intermediate  torrid  zones. 

It  is  a  remarkaljlc  fact,  strongly  insisted  on  by  Hooker  in 
regard  to  America,  and  by  Alph.  de  Candolle  in  regard  to  Aus- 
tralia, that  inany  more  identical  or  now  slightly-modified  spe- 
cies have  migrated  from  the  north  to  the  south,  than  in  a  re- 
versed direction.     We  see,  however,  a  few  southern  forms  on 


348  ALTERNATE  GLACIAL  PERIODS  Chap.  XI. 

tlie  mountains  of  Borneo  and  Abyssinia.  I  suspect  that  this 
preponderant  niij^ration  from  the  north  to  t!ie  south  is  due  to 
the  f^rcatcr  extent  of  hmd  in  the  north,  and  to  tlie  noi'tbeni 
forms  liaviuii;'  existed  in  their  own  homes  in  g-reater  numbers, 
and  havini^  eonsccfucntly  been  advanced  throu<>;h  natural  selec- 
tion and  comjM'tition  to  a  liigher  stage  of  perfection,  or  domi- 
nating jKnver,  tliiui  the  soutliern  forms.  And  thus,  when  the 
two  sets  became  commingled  in  the  equatorial  regions,  during 
the  alternations  of  the  Glacial  periods,  the  northern  forms  were 
the  more  powerful  and  were  able  to  hold  their  places  on  the 
mountains,  and  afterward  to  migrate  southward  with  the  south- 
ern forms ;  but  not  so  the  southern  in  regard  to  the  northern 
forms.  In  the  same  manner  we  see,  at  the  present  day,  that 
very  many  European  productions  cover  the  groimd  in  La  Plata, 
New  Zealand,  and  to  a  lesser  degree  in  Australia,  and  have 
beaten  the  natives  ;  whereas  extremely  few  southern  forms 
have  become  naturalized  in  any  part  of  the  northern  hemisphere, 
though  hides,  wool,  and  other  objects  likely  to  carry  seeds,  have 
been  largely  imported  into  Europe  during  the  last  two  or  three 
ccnturietj  from  La  Plata,  and  during  the  last  thirty  or  forty 
years  from  Australia.  The  Ncilgherric  Mountains  in  India, 
however,  offer  a  part  ial  exception ;  for  here,  as  I  hear  from  Dr. 
Hooker,  Australian  forms  are  rapidly  sowing  themselves  and 
becoming  naturalized.  Before  the  last  great  Glacial  period, 
no  doubt  the  intertropical  mountains  Avere  stocked  with  en- 
demic Alpine  forms  ;  but  these  have  almost  everywhere  yielded 
to  the  more  dominant  forms,  generated  in  the  larger  areas  and 
more  efficient  workshops  of  the  north.  In  many  islands  the 
native  pi'oductions  are  nearly  equalled,  or  even  outnumbered, 
by  those  which  have  become  naturalized ;  and  this  is  the  llrst 
stage  toward  their  extinction.  Mountains  are  islands  on  the 
land,  and  their  inhabitants  have  yielded  to  those  produced  with- 
in the  larger  areas  of  the  north,  just  in  the  same  way  as  the 
inhabitants  of  real  islands  have  everywhere  yielded  and  are 
still  yielding  to  continental  forms  naturalizetl  through  man's 
agency. 

The  same  principles  apply  to  the  distribution  of  terrestrial 
animals  and  of  marine  productions,  in  the  northern  and  south- 
ern temperate  zones,  and  on  the  intertropical  mountains. 
When  during  the  height  of  the  Glacial  period  the  ocean-cur- 
rents Avere  Avidely  diiferent  to  Avhat  thev  noAV  are,  some  of  the 
inhabitants  of  the  temperate  seas  might  have  reached  the  equa- 
tor ;  of  these  a  fcAV  would  perhaps  at  once  be  able  to  migrate 


CiFAP.  XI.  OF  THE  NORTH  AND  SOUTH.  349 

southward,  by  kpcpiiiG^  to  the  cooler  currents,  Avhile  others 
might  remain  and  survive  in  the  cooler  depths,  until  the  south- 
ern hemisphere  was  in  its  turn  subjected  to  a  glacial  climate 
and  permitted  of  their  lurtlier  progress ;  in  nearly  the  same 
manner  as,  accortling  to  Forbes,  isolated  spaces  inhabited  by 
Arctic  productions  exist  to  the  present  day  in  the  deeper  parts 
of  the  temperate  seas. 

I  am  far  from  supposing  that  all  dilhculties  in  regard  to 
the  distribution  and  ailinities  of  the  identical  and  allied  spe- 
cies, which  now  live  so  widely  separated  in  the  north  and 
south,  and  sometimes  on  the  intermediate  mountain-ranges, 
are  removed  on  the  views  above  given.  The  exact  lines  of  mi- 
gration cannot  be  indicated.  We  cannot  say  why  certain  spe- 
cies and  not  others  have  migrated ;  why  certain  species  have 
been  modified  and  have  given  rise  to  new  forms,  while  others 
liave  remained  unaltered.  We  cannot  hope  to  explain  such 
facts,  until  we  can  say  why  one  species  and  not  another  be- 
comes naturalized  l^y  man's  agency  in  a  foreign  land ;  Avhy  one 
species  ranges  twice  or  thrice  as  far,  and  is  twice  or  thrice  as 
common,  as  another  species  within  their  own  homes. 

Various  special  difficulties  also  remain  to  be  solved ;  for  in- 
stance, the  occurrence,  as  shown  by  Dr.  Hooker,  of  tiie  same 
plants  at  points  so  enormously  remote  as  Kerguelen  Land, 
New  Zealand,  and  Fuegia;  but  icebergs,  as  suggested  by  Ly- 
cll,  may  have  l)een  concerned  in  tlieir  dispersal.  The  existence, 
at  these  and  other  distant  points  of  the  southern  hemisphere, 
of  species,  which,  though  distinct,  belong  to  genera  exclusively 
confined  to  the  south,  is  a  more  remarkable  case.  Some  of 
these  species  are  so  distinct,  that  we  cannot  suppose  that  there 
has  been  time  since  the  commencement  of  the  last  Glacial 
period  for  their  migration  and  subsequent  modification  to  the 
necessary  degree.  The  facts  seem  to  me  to  indicate  that  dis- 
tinct species  belonging  to  the  same  genera  have  migrated  in 
radiating  lines  from  a  common  centre ;  and  I  am  inclined  to 
look  in  tiie  southern,  as  in  the  northern  heniisphere,  to  a  former 
and  warmer  ])erio(l,  before  the  commencement  of  the  Ghicial 
period,  when  the  Antarctic  lands,  now  covere^l  with  ice,  sup- 
ported a  liighly  pecuhar  and  isolated  flora.  It  may  be  suspected 
that,  before  this  flora  was  exterminated  during  the  last  Glacial 
epoch,  a  few  forms  had  been  already  widely  dispersed  to  vari- 
ous points  of  the  southern  hemisphere  l)y  occasional  means  of 
transport,  and  by  the  aid,  as  halting-places,  of  now  sunken 
islands.     Thus  tlie  southern  shores  of  America,  Australia,  and 


350  ALTERNATE  GLACIAL  PERIODS.  Cuap.  XI. 

New  Zealand,  niio^'ht  have  become  slightly  tinted  by  the  same 
peculiar  forms  of  life. 

Sir  C.  Lycll  in  a  striking'  passage  has  speculated,  in  lan- 
guage almost  identical  Avith  mine,  on  the  effects  of  great  alter- 
nations of  climate  throughout  the  world  on  geographical  dis- 
tribution. And  we  have  uow  seen  that  Mr.  Oroll's  conclusion, 
that  successive  Glacial  periods  in  the  one  hemisphere  coin- 
cided with  warmer  periods  in  the  opposite  hemisphere,  to- 
gether with  the  admission  of  the  slow  modification  of  species, 
explains  a  multitude  of  facts  in  the  distribution  of  the  same 
and  of  the  allied  forms  of  life  in  all  parts  of  the  globe.  The 
living  waters  have  flowed  during  certain  periods  from  the 
north  and  afterward  from  the  south,  and  in  both  cases  have 
reached  the  equator ;  but  the  stream  of  life  has  flowed  with 
greater  force  from  the  north  than  in  the  opposite  direction,  and 
has  consequently  more  freely  inundated  the  south.  As  the 
tide  leaves  its  drift  in  horizontal  lines,  rising  higher  on  the 
shores  where  the  tide  rises  highest,  so  have  the  Hving  waters 
left  their  living  drift  on  our  mountain-summits,  in  a  line  gently 
rising  from  the  Arctic  lowlands  to  a  great  altitude  under  the 
equator.  The  various  beings  thus  left  stranded  may  be  com- 
pared with  savage  races  of  man,  driven  up  and  surviving  in 
the  mountain-fastnesses  of  almost  every  land,  Avhich  serve  as  a 
record,  full  of  interest  to  us,  of  the  former  inhabitants  of  the 
surroundinjr  lowlands. 


Chat.  XII.  FRESH-WATER  PRODUCTIONS.  851 


CHAPTER  XII. 

GEOGnAPiiicAL  DisTKiBUTiox — Continued. 

Distribution  of  Prcsh-wnfcr  Productions— On  the  Inhabitants  of  Ocranic  IrJlands— 
Absence  of  15atrucl)ian8  and  of  Terrestrial  Mammals— On  the  Relation  of  tlie  In- 
tuibitants  of  I^landx  to  those  of  the  nearest  Main-land— On  Colouizaticm  from  tho 
nearest  Source  with  subsequent  Modification— Summary  of  the  last  and  present 
Chapter. 

Fresh-water  Productions. 

As  lakes  and  river-sj'stenis  arc  separated  from  each  other 
by  barriers  of  land,  it  might  have  been  thought  that  fresh- 
water productions  would  not  have  ranged  widely  within  the 
same  country,  and,  as  the  sea  is  apparently  a  still  more  for- 
midable barrier,  that  they  never  would  have  extended  to  dis- 
tant countries.  But  the  case  is  exactly  the  reverse.  Not  only 
have  many  fresh-water  species,  belonging  to  quite  different 
classes,  an  enormous  range,  but  allied  species  prevail  in  a  re- 
markable manner  throughout  the  world.  I  well  remember, 
when  first  collecting  in  the  fresh  waters  of  Brazil,  feeling  much 
surprise  at  the  similarity  of  the  fresh-water  insects,  shells,  etc., 
and  at  the  dissimilarity  of  the  surrounding  terrestrial  beings, 
compared  with  those  of  Britain. 

But  this  power  in  fresh- water  productions  of  ranging  wide- 
ly, though  so  imcxpected,  can,  I  think,  in  most  cases  be  ex- 
plaiiiod  by  their  having  become  fitted,  in  a  manner  highly 
useful  to  them,  for  short  and  frequent  migrations  from  pond  to 
pond,  or  from  stream  to  stream ;  and  liability  to  wide  disper- 
sal would  follow  from  this  capacity  as  an  almost  necessary  con- 
seipience.  We  can  here  consider  only  a  few  cases.  In  regard 
to  fish,  I  believe  that  the  same  species  never  occur  in  the 
fresh  waters  of  distant  continents.  But  on  the  same  continent 
the  species  often  range  widely  and  almost  capriciously ;  for 
two  river-systems  will  have  some  fish  in  common  and  some 
different.  A  few  facts  seem  to  favor  the  possibility  of  their 
occasi(mal  transport  by  accidental  means ;  like  that  of  the  live 


352  FEESII-WATER  PRODUCTIONS.  Ciixr.  XII. 

fish  not  rarely  dropped  hy  Avhirlwinds  in  India,  and  the  vitality 
t)f  their  ova  when  removed  from  the  Avater.  ]3ut  I  am  inclined 
to  attribute  the  dispersal  of  frcsh-Avater  iish  mainly  to  changes 
in  the  level  of  the  land  within  the  recent  period  having  caused 
rivers  to  flow  into  each  other.  Instances,  also,  coidd  be  given 
of  this  having  occniTcd  during  floods,  without  any  change  of 
level.  The  wide  dilTerence  of  the  fish  on  the  opposite  sides 
of  continuous  mountain-ranges,  -which  from  an  early  period 
must  have  completely  prevented  the  inosculation  of  the  river- 
systems,  seems  to  lead  to  the  same  conclusion.  "With  respect 
to  allied  fresh-water  fish  occurring  at  very  distant  points  of  the 
world,  no  doubt  there  arc  many  cases  which  cannot  at  present 
be  explained  :  but  some  fresh- Avater  fish  belong  to  very  ancient 
fonns,  and  in  such  cases  there  will  have  been  ample  time  for 
great  geograpliical  changes,  and  consequently  time  and  means 
for  such  migration.  In  the  second  place,  salt-water  fish  can 
Avith  care  be  sloAvly  accustomed  to  Ha'c  in  fresh  Avater;  and, 
according  to  Valenciennes,  there  is  hardly  a  single  group  of 
Avhich  all  the  members  are  confined  exclusively  to  fresh  Avatcr, 
so  that  a  marine  species  of  a  frcsh-Avater  group  might  travel 
far  along  the  shores  of  the  sea,  and  subsequently  liecome  modi- 
fied and  adapted  to  the  fresh  Avaters  of  a  distant  land. 

Some  species  of  fresh-Avater  shells  haA'e  A'crA'  Avide  ranges, 
and  allied  species  Avhich,  on  our  theory,  are  descended  from  a 
common  parent,  and  must  haA'C  proceeded  from  a  single  source, 
prevail  throughout  the  Avorld.  Their  distribution  at  first  per- 
plexed me  much,  as  their  OA'a  are  not  likely  to  be  transported 
by  birds,  and  are  immediately  killed  by  sea-Avater,  as  are  the 
adults.  I  could  not  even  understand  hoAV  some  naturalized 
species  have  spread  rapidly  throughout  the  same  country.  But 
tAvo  facts,  Avhich  I  have  observed — and  no  doubt  many  others 
remain  to  be  observed — throAV  some  light  on  this  subject. 
^^'hen  a  duck  suddenly  emerges  from  a  pond  coA'cred  Avith 
duck-Avced,  I  have  tAvicc  seen  these  little  plants  adhering  to 
its  back ;  and  it  has  happened  to  me,  in  remoAing  a  little 
duck-AVoed  from  one  aquarium  to  another,  that  I  have  quite  un- 
intentionally stocked  the  one  Avith  fresh-water  shells  from  the 
other.  13ut  another  agency  is  perhaps  more  eftectual :  I  sus- 
pended a  duck's  feet  in  an  aquarium,  Avhere  many  ova  of  fresh- 
Avater  shells  Avere  hatching ;  and  I  found  that  numbers  of  the 
extremely  minute  and  just-hatched  shells  craAvled  on  the  feet, 
and  clung  to  them  so  firmly  that,  Avhen  taken  out  of  the  Avater, 
they  could  not  be  jarred  off,  though  at  a  someA\hat  more  ad- 


CuAr.  XII.  FRESn-WATER  PRODUCTIONS.  353 

vanced  a;^c  ihoy  would  voluntarily  drop  olT.  These  just- 
hatched  moUusks,  thoui^h  aquatic  in  their  nature,  survived  on 
the  duck's  feet,  in  damp  air,  from  twelve  to  twenty  hours ;  and 
in  this  lenp^tli  of  time  a  duck  or  heron  mij^ht  (ly  at  least  six  or 
seven  hundred  miles,  and,  if  blown  across  the  sea  to  an  oceanic 
island  or  to.  any  other  distant  point,  would  be  sure  to  alight  on 
a  pool  or  rivulet.  Sir  Charles  Lyell  informs  me  that  a  Dj'tiscus 
has  been  cau2;ht  with  an  Ancylus  (a  fresh-water  shell  like  a 
limpet)  firmly  adhering-  to  it ;  and  a  Avater-beetle  of  the  same 
family,  a  Colymbetes,  once  flew  on  board  the  "  Beagle,"  when 
forty-five  miles  distant  from  the  nearest  land :  how  much 
farther  it  might  have  been  blown  with  a  favoring  gale  no  one 
can  tell. 

With  respect  to  plants,  it  has  long  been  known  what 
enormous  ranges  many  fresh-water,  and  even  marsh-species, 
have,  both  over  continents  and  to  the  most  remote  oceanic 
isFands,  This  is  strikingly  shown,  as  remarked  by  Alph.  de 
Candolle,  in  large  groups  of  terrestrial  plants,  ^vluc]l  have  only 
a  very  few  aquatic  members  ;  for  these  latter  seem  immediate- 
ly to  acquire,  as  if  in  consequence,  a  very  wide  range.  I 
think  favorable  means  of  dispersal  explain  this  fact.  I  have  be- 
fore mentioned  that  earth  occasionally,  though  rarely,  adheres 
in  some  quantity  to  the  feet  and  beaks  of  birds.  Wading- 
birds,  which  frequent  the  muddy  edges  of  ponds,  if  suddenly 
flushed,  would  be  the  most  likely  to  have  muddy  feet.  Birds 
of  this  order,  I  can  show,  arc  the  greatest  wanderers,  and  are 
occasionally  found  on  the  most  remote  and  barren  islands  in 
the  open  ocean ;  they  would  not  be  likely  to  alight  on  the  sur- 
face of  the  sea,  so  that  the  dirt  would  not  be  washed  off  their 
feet ;  and,  when  making  land,  they  would  be  sure  to  fly  to  their 
natural  fresh-water  haunts.  I  do  not  believe  that  botanists 
an;  aware  how  charged  the  mud  of  ponds  is  with  seeds :  I 
have  tried  several  little  experiments,  l)ut  will  here  give  only 
the  most  striking  case  :  I  took  in  February  three  table-spoon- 
fuls of  mud  from  three  different  points,  beneath  water,  on  the 
edge  of  a  little  pond:  this  mud  when  dry  weighed  only  GJ 
ounces  ;  I  kcjit  it  covered  up  in  my  study  for  six  months,  pull- 
ing up  and  CHjunting  each  plant  as  it  grew ;  the  plants  were 
f)f  many  kinds,  and  were  altogether  537  in  number;  and  yet 
the  viscid  mud  was  all  contiiined  in  a  breakfast  cup  !  Consid- 
ering these  facts,  I  think  it  would  be  an  inexplic;d)l(>  circum- 
stance if  water-birds  did  not  transport  the  seeds  of  the  same 
fivsh-water  plants  to  unstocked  ponds  and  streams,  situated  at 


364  FRESU-WATEK  PRODUCTIONS.  Chap,  XII. 

very  distant  points.  The  same  ag'ency  may  lia\'C  come  into 
play  with  tlic  e<xgs  of  some  of  the  smaller  fresh-water  animals. 

Other  and  unknown  agencies  probably  have  also  played  a 
part.  I  have  stated  that  fresh-water  fish  eat  some  kinds  of 
seeds,  though  they  reject  man}'  other  lands  after  having  swal- 
lowed them  ;  even  small  fish  swallow  seeds  of  moderate  size, 
as  of  tlie  yellow  water-lily  and  Potamogeton.  Herons  and 
other  birds,  century  after  century,  have  gone  on  daily  devour- 
ing fish  ;  they  then  take  flight  and  go  to  other  waters,  or  are 
blown  across  the  sea  ;  and  Ave  have  seen  that  seeds  retain  their 
power  of  germination,  when  rejected  in  pellets  or  in  excre- 
ment, many  hours  afterward.  AVhen  I  saw  the  great  size  of 
the  seeds  of  that  fine  water-lily,  the  Nelumbium,  and  remem- 
bered Alph.  de  Candolle's  remarks  on  this  plant,  I  thought 
that  its  distribution  must  remain  quite  inexplicable  ;  but 
Audubon  states  that  he  found  the  seeds  of  the  great  southern 
water-lily  (probably,  according  to  Dr.  Hooker,  the  Nelumbium 
luteum)  in  a  heron's  stomach  ;  although  I  do  not  know  the 
fact,  yet  analogy  makes  me  believe  that  a  heron,  fl^'ing  to  an- 
other pond  and  getting  a  heai-ty  meal  of  fish,  Avould  probably 
reject  from  its  stomach  a  pellet  containing  the  seeds  of  the 
Nelumbium  undigested  ;  or  the  seeds  might  be  dropped  by  the 
bird  Avhile  feeding  its  young,  in  the  same  way  as  fish  are  known 
sometimes  to  be  dropped. 

In  considering  these  several  means  of  distribution,  it  shoukl 
be  remembered  that  Avhen  a  pond  or  stream  is  first  formed,  for 
instance,  on  a  rising  islet,  it  Avill  be  unoccupied ;  and  a  single 
seed  or  e^^g  will  have  a  good  chance  of  succeeding.  Although 
there  Anil  always  be  a  struggle  for  life  between  the  inhabitants 
of  the  same  pond,  hoAvever  few  in  Idnd,  yet,  as  the  number  even 
in  a  Avell-stocked  pond  is  small  in  comparison  Avitli  the  number 
of  species  inhabiting  an  equal  area  of  land,  the  competition 
Avill  probably  be  less  severe  between  aquatic  than  betAveen  ter- 
restrial species ;  consequently  an  intruder  from  the  waters  of 
a  foreign  country  Avillhave  a  better  chance  of  seizing  on  a  ncAV 
place,  than  in  the  case  of  terrestrial  colonists.  We  should  also 
remember  that  many  frcsh-AAMter  productions  are  low  in  the 
scale  of  nature,  and  Ave  have  reason  to  believe  that  Ioav  beings 
change  or  become  modified  less  quickl}^  than  the  high  ;  and  this 
Avill  giA'e  a  longer  time  than  the  aA'erage  for  the  rj;igration  of 
the  same  aquatic  species.  We  should  not  forget  the  probability 
of  many  species  having  formerly  ranged  as  continuously  as 
fresh-Avater  productions  ever  can  range,  over  immense  areas 


Chap.  XI [.         INHABITANTS  OF  OCEANIC  ISLANDS.  355 

and  having  subseqiienlly  become  extinct  in  intermediate  re- 
gions. But  the  wide  distribution  of  fresli-wuter  pkxnts  and  of 
the  lower  animals,  whether  retaining  the  same  identical  form 
or  in  some  degree  modifieJ,  I  believe  mainly  depends  on  the 
wide  disjiersal  of  their  seeds  and  eggs  by  animals,  more  es- 
pecially by  fresh-water  birds,  which  have  great  poAvers  of 
flight,  and  naturally  travel  from  one  piece  of  water  to  another. 

On  the  InJuihltayds  of  Oceanic  Islcmds. 

We  now  come  to  the  last  of  the  three  classes  of  facts, 
which  I  have  selected  as  presenting  the  greatest  amount  of 
dilliculty,  if  we  accept  the  view  that  not  only  all  the  individ- 
uals of  the  same  species,  wherever  found,  have  migrated  from 
some  one  area,  but  that  allied  species,  although  now  inhabiting 
the  most  distant  points,  have  proceeded  from  a  single  area — 
tlie  birthplace  of  their  early  prog(Miitor.  I  have  already  stated 
that  I  cannot  honestly  admit  For])es's  view  en  continental  ex- 
tensions, which,  if  legitimately  followed  out,  would  lead  to  the 
belief  that  all  existing  islands  have  been  continuously  or 
almost  continuously  joined  to  some  continent  within  the  recent 
period.  This  view  Avould  remove  many  dilliculties,  but  it 
would  not  explain  all  the  facts  in  regard  to  insular  produc- 
tions. In  the  following  remarks  I  shall  not  confine  myself  to 
the  mere  question  of  dispersal ;  but  shall  consider  some  other 
facts,  which  bear  on  the  truth  of  the  two  theories  of  indepen- 
dent creation  and  of  descent  with  modification. 

The  species  of  all  kinds  which  inhabit  oceanic  islands  are 
few  in  number  compared  Avith  those  on  equal  continental 
areas :  Alph.  de  Candolle  admits  this  for  plants,  and  AVollas- 
ton  for  insects.  New  Zealand,  for  instance,  with  its  lofty 
moimlains  and  diversified  stations,  extending  over  780  miles 
of  latitufle,  together  with  the  outlying  islands  of  Auckland, 
Campbell,  and  Chatham,  contain  altogether  only  DCO  lands 
of  flowering  plants;  if  we  compare  this  moderate  number  with 
the  species  which  swann  over  equal  areas  in  Southwestern 
Australia  or  at  the  Cape  of  Good  Ilojie,  we  nnist  admit  that 
somclliing,  quite  indcpenilently  of  a  difVerence  in  tlie  ])hvsical 
conditions,  has  caused  so  great  a  difVerence  in  number.  Even 
the  uniform  county  of  Cambridge  has  847  plants,  and  the  little 
island  of  Anglesea  704,  but  a  few  ferns  and  a  few  introduced 
plants  are  included  in  these  nundiers,  and  the  comparison  in 
some  other  respects  is  not  quite  fair,     "\\'e  have  evidence  that 


350  INHABITANTS  OF  OCEANIC  ISLANDS.         Cuai-.  XII. 

the  barren  isluiul  of  Ascension  aboriginally  possessed  less  than 
half  a  dozen  lowering  plants  ;  yet  many  have  now  become 
naturalized  on  it,  as  they  have  on  New  Zealand  and  on  every 
other  oceanic  island  Avhich  can  be  named.  In  St.  Helena  there 
is  reason  to  believe  that  the  naturalized  plants  and  animals 
have  nearly  or  quite  exterminated  many  native  productions. 
He  who  admits  the  doctrine  of  the  creation  of  each  separate 
species,  will  have  to  admit  that  a  sufficient  number  of  the  best 
adapted  plants  and  animals  were  not  created  for  oceanic 
islands ;  for  man  has  unintentionally  stocked  them  far  more 
fully  and  perfectly  than  did  Nature. 

Although  in  oceanic  islands  the  species  are  few  in  number, 
the  proportion  of  endemic  kinds  (i.  e.,  those  found  nowhere 
else  in  the  Avorld)  is  often  extremely  large.  If  Ave  compare, 
for  instance,  the  number  of  endemic  land-shells  in  Madeira,  or 
of  endemic  birds  in  the  Galapagos  Archipelago,  Avith  the  num- 
ber found  on  any  continent,  and  then  compare  the  area  of  the 
island  Avith  that  of  the  continent,  Ave  shall  see  that  this  is  true. 
This  fact  might  have  been  theoretically  expected,  for,  as  al- 
ready explained,  species  occasionally  arriving  after  long  inter- 
A'als  of  time  in  a  ncAV  and  isolated  district,  and  having  to  com- 
pete AA'ith  ncAV  associates,  Avould  be  eminently  liable  to  modifi- 
cation, and  Avould  often  produce  groups  of  modified  descend- 
ants. But  it  by  no  means  folloAvs  that,  because  in  an  island 
nearly  all  the  species  of  one  class  are  peculiar,  those  of  an- 
other class,  or  of  another  section  of  the  same  class,  are  pecu- 
liar ;  and  this  difference  seems  to  depend  partly  on  the  species 
Avhich  are  not  modified  having  immigrated  in  a  body,  so  that 
their  mutual  relations  haA^e  not  been  much  disturbed;  and 
partly  on  the  frequent  arrival  of  immodified  immigrants  from 
the  mother-country,  Avith  Avhich  the  insular  forms  have  inter- 
crossed. It  should  be  borne  in  mind  that  the  offspring  of  such 
crosses  AA'ould  almost  certainly  gain  in  vigor  ;  so  that  even  an 
occasional  cross  AA'ould  produce  more  effect  than  might  have 
been  anticipated.  I  Avill  give  a  fcAV  illustrations  of  the  forego- 
ing remarks  :  in  the  Galapagos  Islands  there  are  20 land-birds; 
of  these,  21  (or  perhaps  23)  are  peculiar,  AA'hereas  of  the  11 
marine  birds  only  2  are  peculiar ;  and  it  is  obvious  that  marine 
lairds  could  arrive  at  these  islands  much  more  easily  and  fre- 
quently than  land-birds.  Bermuda,  on  the  other  hand,  Avhich 
lies  at  about  the  same  distance  from  North  America  as  the 
Galapagos  Islands  do  from  South  America,  and  Avhich  has  a 
A'cry  peculiar  soil,  does  not  possess  a  single  endemic  land-bird ; 


CiiAr.  XII.        INHABITANTS  OF  OCEANIC  ISLANDS.  357 

and  we  know,  from  Mr.  J.  M.  Jones's  admirable  account  of  Ber- 
muda, that  very  many  North  American  birds  occasional!}'  or 
even  frequently  visit  this  island.  Almost  every  year,  as  I  am 
informed  l)y  !Mr.  E.  V.  Harcourt,  many  EuropeaTi  and  African 
birds  arc  blown  to  Madeira ;  this  island  is  inhaljited  by  99 
kinds,  of  which  one  alone  is  peculiar,  though  very  closely 
related  to  a  European  form  ;  and  three  or  four  other  species 
are  confined  to  this  island  and  to  the  Canaries.  So  that  the 
islands  of  13ermuda  and  Madeira  have  been  stocked  from  the 
neighboring  continents  with  birds,  whicli  for  long  ages  have 
struggled  together,  and  become  mutually  adapted ;  hence, 
when  settled  in  their  new  homes,  each  kind  wduld  be  kept  by 
the  others  to  its  proper  place  and  habits,  and  would  conse- 
quently be  but  little  liable  to  modification.  Any  tendency  to 
modification  would  also  be  checked  by  intercrossing  with  the 
unmodified  immigrants  from  the  mother-country.  Madeira, 
again,  is  inhabited  by  a  wonderful  lumiber  of  peculiar  land- 
sliells,  whereas  not  one  species  of  sea-shell  is  peculiar  to  its 
shores :  now,  though  we  do  not  know  how  sea-shells  are  dis- 
persed, yet  we  can  sec  that  their  eggs  or  larva?,  perhaps  at- 
tached to  seaweed  or  floating  timber,  or  to  the  feet  of  wading- 
birds,  might  be  transported  across  three  or  four  hundi'cd  miles 
of  open  sea  far  more  easily  than  land-shells.  Tlie  dilTerent 
orders  of  insects  inhabiting  Madeira  present  nearly  similar 
cases. 

Oceanic  islands  are  sometimes  deficient  in  animals  of  cer- 
tain Avhole  classes,  and  their  places  are  occupied  by  other 
classes:  thus  in  the  Galapagos  Islands  reptiles,  and  in  New 
Zealand  gigantic  wingless  birds,  take,  or  recently  took,  the 
j)lace  of  mammals.  Altliough  New  Zealand  is  here  spoken  of 
as  an  oceanic  island,  it  is  in  some  degree  doubtful  whether  it 
should  1)0  so  ranked ;  it  is  of  large  size,  and  is  not  separated 
from  Australia  by  a  profoundly  deep  sea;  from  its  geological 
character  and  tlie  direction  of  its  mountain-ranges,  the  Rev. 
W.  15.  Clarke  has  lately  maintained  that  this  island,  as  well 
as  New  Caledonia,  should  be  considered  as  appurtenances  of 
Australia.  Turning  to  plants.  Dr.  Hooker  has  shown  that  in 
the  Galapagos  Islands  tlie  ])roportional  numbers  of  the  difl'er- 
ent  orders  are  very  different  from  what  they  are  elsewhere. 
All  such  diflerences  in  luimber,  and  the  absence  of  certain 
whole  grou]\s  of  animals  and  jilants  on  islands,  are  gtMierally 
account(>d  for  by  su]iposed  ditVerences  in  their  ])hysical  condi- 
tions; but  this  explanation  is  not  a  little  doubtful.     Facility 


358  ABSENCL  OF  TERKESTEIAL  MAMMALS       Chap.  XII. 

of  inimioTalion  seoins  to  liavc  been  fully  as  impoptant  as  the 
nature  of  the  conditions. 

JIany  remarkable  little  facts  could  bo  given  with  respect  to 
the  inhabit:iuts  of  oceanic  islands.  For  instance,  in  certain 
islands  not  tenanted  Iiy  a  sing-le  mammal,  some  of  the  endemic 
plants  have  beautifully  hooked  seeds;  and  few  relations  arc 
more  manifest  than  that  hooked  seeds  are  adapted  for  trans- 
portal  in  the  wool  or  fin-  of  quadi-upeds.  But  a  hooked  seed 
might  be  carried  to  an  island  by  other  means ;  and  the  plant 
then  becoming  modified  Avould  form  an  endemic  species,  Avhich 
might  still  retain  the  hooks,  Avhich  would  not  form  a  more  use- 
less appendage  than  the  shrivelled  wings  imder  the  soldered 
elytra  of  many  insular  beetles.  Again,  islands  often  possess 
trees  or  bushes  belonging  to  orders  elsewhere  including  only 
herbaceous  species ;  now  trees,  as  Alph.  de  Candolle  has  shown, 
generally  have,  whatever  the  cause  may  be,  confined  ranges. 
Hence  trees  Avould  be  little  likely  to  reach  distant  oceanic 
islands  ;  and  an  herbaceous  plant,  which  had  no  chance  of  suc- 
cessfully competing  Avitli  the  many  fully-developed  trees  grow- 
ing on  a  continent,  might,  when  established  on  an  island,  gain 
an  advantage  by  growing  taller  and  taller  and  overtopping  the 
other  herbaceous  plants.  In  this  case,  natural  selection  would 
tend  to  add  to  the  stature  of  the  plant,  to  whatever  order  it 
belonged,  and  thus  convert  it  first  into  a  bush  and  then  into  a 
tree. 

Absence  of  Batrachians  and  Terrestrial  j[Tammals  on  Oce- 
anic Islands. 

"With  resjiect  to  the  absence  of  whole  orders  of  animals  on 
oceanic  islands,  I5ory  St.  Vincent  long  ago  remarked  that  Ba- 
trachians (frogs,  toads,  newts)  are  never  found  on  any  of  the 
many  islands  with  which  the  great  oceans  are  studded.  I  have 
taken  pains  to  verify  this  assertion,  and  have  found  it  strictly 
true,  with  the  exception  of  New  Zealand,  of  the  Andaman 
Islands,  and  perhaps  of  the  Salomon  Islands.  But  I  have  al- 
ready remarked  that  it  is  doubtful  whether  New  Zealand  ought 
to  be  classed  as  an  oceanic  island ;  and  this  is  still  more  doubt- 
ful with  respect  to  the  Andaman  and  Salomon  groups.  This 
general  absence  of  frogs,  toads,  and  newts,  on  so  many  oceanic 
islands  cannot  be  accounted  for  by  their  physical  conditions; 
indeed,  it  seems  that  islands  are  peculiarly  well  fitted  for  these 
animals:    for  frogs  have    been    introduced  into  Madeira,   the 


Chap.  XII.  ON  OCEANIC  ISLANDS.  359 

Azores,  and  Mauritius,  and  liavo  multiplied  so  as  to  become  a 
nuisance.  But,  as  these  animals  ami  their  spawn  are  known  to 
be  immediately  killed  hy  sea-wat<^r,  there  wovdd  be  great  dilfi- 
culty  in  their  transportal  across  the  sea,  and  therefore  we  can 
sec  why  they  do  not  exist  on  any  oceanic  island.  But  why,  on 
tlie  theory  of  creation,  they  should  not  have  been  created  there, 
it  would  be  very  dillicult  to  explain. 

Mammals  ofler  another  and  similar  case.  I  have  carefully 
searched  the  oldest  voyao-es,  and  as  yet  I  have  not  found  a 
single  instance,  free  frt)m  doubt,  of  a  terrestrial  mammal  (ex- 
cluding domesticated  animals  kept  by  the  natives)  inhabiting' 
an  island  situated  above  300  miles  from  a  continent  or  great 
continental  island ;  and  many  islands  situated  at  a  much  less 
distance  are  equally  l)arren.  The  Falkland  Islands,  which  are 
inhabited  by  a  wolf-like  fox,  come  nearest  to  an  exception  ;  but 
tlws  group  cannot  be  considered  as  oceanic,  as  it  lies  on  a  bank 
in  connection  with  the  main-land  at  the  distance  of  about  280 
miles ;  moreover,  icebergs  formerly  brought  bowlders  to  its 
western  shores,  and  they  may  have  formerly  transported  foxes, 
as  now  frequently  happens  in  the  arctic  regions.  Yet  it  cannot 
be  said  that  small  islands  will  not  support  at  least  small  mam- 
mals, for  they  occur  in  many  parts  of  the  world  on  very  small 
islands,  when  lying  close  to  a  continent;  and  hardly  an  island 
can  be  named  on  which  oin-  smaller  quadrupeds  have  not  be- 
come naturalized  and  greatly  nuiltiplicd.  It  capnot  be  said, 
on  the  ordinary  view  of  creation,  tliat  there  has  not  been  time 
for  the  creation  of  mammals;  many  volcanic  islands  are  sufTi- 
ciently  ancient,  as  shown  l)y  the  stupendous  degradation  which 
they  have  suffered,  and  by  their  tertiary  strata :  there  has  also 
bcHMi  time  for  the  production  of  endemic  species  belonging  to 
other  classes  ;  and  on  continents  it  is  known  that  mammals  ap- 
pear and  disappear  at  a  quicker  rate  than  any  other  and  lower 
animals.  Although  terrestrial  mammals  do  not  occur  on  oce- 
anic islands,  aerial  mammals  do  occur  on  almost  every  island. 
New  Zealand  possesses  two  bats  found  nowhere  else  in  the 
■world  :  Norfolk  Island,  the  Viti  Archipelago,  the  Bonin  Islands, 
the  Caroline  and  Mariannt"  Archipelagoes,  and  Mauritius, 
all  possess  their  jieculiar  bats.  N\  hy,  it  may  be  asked,  has 
the  supposed  creative  force  ])roduced  bats  and  no  other  mam- 
mals on  remote  islands  ?  On  my  view  this  (juestion  can  easily 
be  answered;  for  no  terrestrial  mammal  can  be  transported 
across  a  wide  space  of  sea,  but  bats  can  fly  across.  Bats  have 
been  seen  wandering  by  d:iy  far  over  the  Atlantic  Ocean;  and 


3 GO  ABSENCE  OF  TERKESTKIAL  MAMMALS       Chap.  XII. 

two  North  American  species  either  ref^ularly  or  occasionally 
visit  Bermuda,  at  the  distance  of  GOO  miles  from  the  main-land. 
I  hear  from  Mr.  Tomes,  who  has  specially  studied  this  family, 
that  many  species  have  enormous  ranj^es,  and  are  found  on  con- 
tinents and  on  far-distant  islands.  Hence  we  have  only  to  sup- 
pose that  such  wandering  species  have  been  modified  in  their 
new  homes  in  relation  to  their  new  position,  and  we  can  under- 
stand the  presence  of  endemic  bats  on  oceanic  islands,  with  the 
absence  of  all  other  terrestrial  mammals. 

Another  interesting  relation  exists,  namely,  between  the 
depth  of  the  sea  separating  islands  from  each  other  or  from  the 
nearest  continents,  and  the  degree  of  affinity  of  their  mamma- 
lian inhabitants.  Mr.  Windsor  Earl  has  made  some  striking 
observations  on  this  head,  since  greatly  extended  by  Mr.  Wal- 
lace's admirable  researches,  in  regard  to  the  great  Malay  Ar- 
chipelago, which  is  traversed  near  Celebes  by  a  space  of  deep 
ocean,  and  tliis  separates  two  widely-distinct  mammalian  fau- 
nas. On  either  side  the  islands  stand  on  a  moderately  shallow 
submarine  bank,  and  these  are  inhabited  by  the  same  or  by 
very  closely-allied  quadrupeds.  I  have  not  as  yet  had  time  to 
follow  uj")  this  subject  in  all  quarters  of  the  world ;  but,  as  far 
as  I  have  gone,  the  relation  generally  holds  good.  For  in- 
stance, Britain  is  separated  by  a  shallow  channel  from  Europe, 
and  the  mammals  are  the  same  on  both  sides  ;  and  so  it  is  with 
all  the  islands  near  the  shores  of  Australia.  The  West-Indian 
Islands,  on  the  other  hand,  stand  on  a  deeply-submerged  bank, 
nearly  1,000  fathoms  in  depth,  and  here  we  find  American 
forms,  but  the  species  and  even  the  genera  arc  quite  distinct. 
As  the  amount  of  modification  which  animals  of  all  kinds  un- 
dergo partly  depends  on  the  lapse  of  time,  and  as  islands  sep- 
arated from  each  other  or  from  the  main-land  by  shallow  chan- 
nels are  more  likely  to  have  been  continuously  united  within  a 
recent  period  than  islands  separated  by  deeper  channels,  we 
can  imdcrstand  how  it  is  that  a  relation  exists  l)etween  the 
depth  of  the  sea  separating  two  mammalian  fiiimas,  and  the  de- 
gree of  their  affinity — a  relation  which  is  quite  inexplicable  on 
the  theory  of  independent  acts  of  creation. 

The  foregoing  statements  in  regard  to  the  inhabitants  of 
oceanic  islands — namelv,  the  fewness  of  the  species,  with  a 
large  proportion  consisting  of  endemic  forms — the  members 
of  certain  groups,  and  not  of  other  groups  in  the  same  class, 
having  hoen  modified — the  absence  of  certain  whole  orders,  as 
of  batrachians  and  of  terrestrial  mammals,  notwithstanding  the 


CuAP.  XII.  ON  OCEANIC  ISLANDS.  301 

presence  of  aerial  bats — the  singular  proportions  of  certain 
orders  of  plants — herbaceous  forms  having  been  develoi)cd  into 
trees,  etc.,  seem  to  me  to  accord  better  with  the  belief  in  the 
cfiiciency  of  occasional  means  of  transport,  carried  on  during  a 
long  course  of  time,  than  Avith  the  belief  in  the  former  connec- 
tion of  all  oceanic  islands  with  the  nearest  continent ;  for,  on 
this  latter  view,  it  is  probable  that  the  various  classes  would 
have  immigrated  more  uniformly,  and,  from  the  species  having 
entered  in  a  body,  their  mutual  relations  would  not  have  been 
much  distiu-bed,  and  consequently  tliey  would  have  been  modi- 
fied citlier  not  at  all  or  in  a  more  equal  manner. 

I  do  not  deny  that  there  arc  many  and  serious  difficulties 
in  understanding  how  many  of  the  inhabitants  of  the  more 
remote  ishxnds,  whether  still  retaining  the  same  specific  form 
or  subsequently  modified,  have  reached  their  present  homes. 
Hut  the  probability  of  islands  having  existed  as  halting-places, 
of  which  not  a  wreck  now  remains,  must  not  he  overlooked. 
T  will  specify  one  such  dillicult  case.  Almost  all  oceanic 
islands,  even  the  most  isolated  and  smallest,  are  inhabited  l)y 
land-shells,  generally  by  endemic  species,  but  sometimes  l)y 
species  found  elsewhere — striking  instances  of  which  have 
been  given  by  Dr.  A.  A.  Gould  in  relation  to  the  Pacific. 
Kow,  it  is  notorious  that  land-shells  are  easily  killed  by  sea- 
water;  their  eggs,  at  least  such  as  I  have  tried,  sink  in  it  and 
are  killed.  Yet  there  must  l)e,  according  to  our  view,  some 
luiknown,  but  occasionally  eflicient,  means  for  their  trauspor- 
tal.  ^Vould  the  just-hatched  young  sometimes  adhere  to  the 
fe(>t  of  l)irds  roosting  on  the  ground,  and  thus  get  transported? 
It  occurred  to  me  that  land-shells,  when  hj'bcrnating,  and  hav- 
ing a  nuMnljranous  dia]ihragm  over  the  mouth  of  the  shell, 
might  be  floated  in  chinks  of  drifted  tunl)er  across  moderately 
wide  arms  of  the  sea.  And  I  found  that  several  species  in  this 
state  withstood  uninjured  an  immersion  in  sea-water  during 
seven  days  :  one  shell,  the  Helix  pomatia,  after  having  been 
thus  treated  and  again  hybernating,  was  put  into  sea-water  for 
twenty  da\s,  and  ])erfectly  recovered.  During  tliis  length  of 
time  tlie  shell  might  have  been  carried,  by  a  marine  current  of 
average  sv.iftness,  to  a  distance  of  GGO  geogra])liical  miles. 
As  this  Helix  has  a  thick  calcareous  operculum,  I  removed  it, 
and,  when  it  had  formed  a  new  membranous  one,  I  again  im- 
mersed it  for  fourteen  days  in  se:irwater,  and  again  it  recov- 
ered and  crawled  away.  Baron  Aucapitaine  has  recently  tried 
similar  experiments:  he  placed  100  land-shells,  belonging  to 
IG 


3C2  RELATIONS  OF  THE  INHABITANTS  OF        Chap.  XII. 

ten  species,  in  :i  ])ox  pierced  with  holes,  and  immersed  it  for  a 
fortnight  in  the  sea.  Out  of  the  hundred  shells,  twenty-seven 
recovered.  The  presence  of  an  ojierculum  seems  to  have  been 
of  importance,  as  out  of  twelve  sj^ecimcns  of  Cydostoma  cle- 
gans,  which  is  thus  furnished,  eleven  revived.  It  is  remarkable, 
seeing  how  well  with  me  the  Helix  pomatia  resisted  the  salt- 
water, that  not  one  of  fifty-four  specimens,  l^elonging  to  four 
species  of  Helix  tried  by  Aueapitaine,  recovered.  It  is,  how- 
ever, not  at  all  probable  that  land-shells  have  often  been  thus 
transported  ;  the  feet  of  birds  is  a  more  probable  method. 

On  the  Relations  of  the  Inhabitants  of  Islaiids  to  those  oftJie 
nearest  Main-land. 

The  most  striking  and  important  fact  for  us  is  the  affinity 
of  the  species  which  inhabit  islands  to  those  of  the  nearest 
main-land,  without  being  actually  the  same.  Numerous  in- 
stances could  be  given.  The  Galapagos  Archipelago,  situated 
under  the  equator,  lies  at  the  distance  of  between  500  and  GOO 
miles  from  the  shores  of  Soutli  America.  Here  almost  every 
jiroduct  of  the  land  and  the  water  l)ears  the  unmistakable 
stamp  of  the  American  Continent.  There  are  twenty-six  land- 
birds,  and  twenty-one,  or,  perhaps,  twenty-three,  of  these  arc 
)"anked  as  distinct  species,  and  are  supposed  to  have  been 
created  here ;  yet  the  close  affinity  of  most  of  these  birds  to 
American  species  in  every  character,  in  their  habits,  gestures, 
and  tones  of  A^oice,  was  manifest.  So  it  is  with  the  other  ani- 
mals, and  with  a  large  proportion  of  the  plants,  as  shown  by 
Dr.  Hooker  in  his  admirable  Flora  of  this  archipelago.  The 
naturalist,  looking  at  the  inhabitants  of  these  volcanic  islands 
in  the  Pacific,  distant  several  hundred  miles  from  the  continent, 
yet  feels  that  he  is  standing  on  American  land.  Why  should 
this  be  so  ?  why  should  the  species  which  are  supposed  to 
have  been  created  in  the  Galapagos  Archipelago,  and  nowhere 
else,  bear  so  plain  a  stamp  of  affinity  to  those  created  in  Amer- 
ica ?  There  is  nothing  in  the  conditions  of  life,  in  the  geologi- 
cal nature  of  the  islands,  in  their  height  or  climate,  or  in  the 
proportions  in  which  the  several  classes  are  associated  to- 
gether, which  closely  resembles  the  conditions  of  the  South 
American  coast :  in  fact,  there  is  a  considerable  dissimilarity 
in  all  the  foregoing  respects.  On  the  other  hand,  there  is  a 
considerable  degree  of  resemblance  in  the  volcanic  nature  of 
the  soil,  in   the   climate,  height,  and   size  of   the  islands,   be- 


Chap.  XII.    ISLANDS  TO  THOSE  OF  THE  MAIN-LANJ).  303 

twccn  the  Galap.'ifjos  aiul  Capo  dc  Verde  Arcliipclaii-oes :  but 
Avhat  an  entire  and  absolute  difTorence  in  their  inlialjitants ! 
The  inliabitants  of  the  Cape  de  Verde  Islands  are  related  to 
those  of  Africa,  like  those  of  the  Galapagos  to  America. 
Facts  such  as  these  admit  of  no  sort  of  explanation  on  the 
ordinary  view  of  independent  creation  ;  whereas,  on  the  view, 
here  maintained,  it  is  obvious  that  the  Galapagos  Islands 
would  be  likely  to  receive  colonists,  whether  by  occasional 
means  of  transport  or  by  formerly  continuous  land,  fi'om  Amer- 
ica ;  the  Cape  de  Verde  Islands  from  Africa  :  and  that  such 
colonists  would  be  liable  to  modification — the  principle  of  in- 
heritance still  betraving  their  original  birthplace. 

Many  analogous  facts  could  be  given :  indeed,  it  is  an  al- 
most universal  rule  that  the  endemic  productions  of  islands 
are  related  to  those  of  the  nearest  continent,  or  of  the  nearest' 
island.  The  exceptions  are  few,  and  most  of  them  can  be 
explained.  Thus,  although  Kerguelen  Land  stands  nearer  to 
Africa  than  to  America,  the  plants  are  related,  and  that  very 
closely,  as  we  know  from  Dr.  Hooker's  accoimt,  to  those  of 
America :  but,  on  the  view  that  this  island  has  been  mainly 
stocked  by  seeds  brought  with  earth  and  stones  on  icel)ergs, 
drifted  by  the  prevailing  currents,  this  anomaly  disappears. 
New  Zealand  in  its  endemic  plants  is  much  more  closely  re- 
lated to  Australia,  tlie  nearest  main-land,  than  to  any  other 
region:  and  this  is  what  might  have  been  ex])ccted  ;  but  it  is 
also  plainly  related  to  South  America,  which,  although  the 
next  nearest  continent,  is  so  enormously  remote,  that  the  fact 
becomes  an  ancjinaly.  But  this  difFiculty  almost  disajipears  on 
the  view  that  New  Zealand,  South  America,  and  tlie  other 
southern  lands,  have  been  partially  stocked  from  a  nearly  in- 
termediate though  distant  point,  namely,  from  the  antaictic 
islands,  when  they  were  clothed  with  vegetation,  during  a 
warmer  tertiary  period,  before  the  commencement  of  the  last 
Glacial  period.  The  allinity,  which,  though  feeble,  I  am 
assured  by  Dr.  Hooker  is  real,  between  the  flora  of  the  S(juth- 
western  corner  of  Australia  and  of  the  Ca]ie  of  Good  Ilojie,  is 
a  far  more  remarkable  case  ;  but  this  ailinity  is  ccmlined  to  the 
])lan(s,  and  will,  no  doubt,  be  some  day  explained. 

The  same  law  which  has  determined  the  relati(mshi|)  be- 
tween the  inhabitants  of  islands  and  the  nearest  main-land  i.s 
sometimes  displayed  on  a  small  scale,  but  in  a  most  interesting 
manner,  within  tlie  limits  of  the  same  archipelago.  Thus  each 
separate  island  of  the  Galapagos  Archipelago  is  ti-nanted,  and 


564  EELATIONS  OF  TlIK  INHABITANTS  OF        Chap.  XII. 

the  fact  is  a  iiiarvcllous  ono,  by  distinct  species;  but  these 
species  arc  related  in  a  very  much  closer  manner  to  each  other 
than  to  the  inhabitants  of  any  other  quarter  of  the  world.  Tliis 
is  what  mii^ht  have  been  expected,  for  islands  situated  so  near 
each  other  would  almost  necessarily  receive  immi<Ti"ants  from 
the  same  orig'inal  source,  and  from  each  other.  But  how  is  it 
that  many  of  the  immif^rants  have  been  differently  modified, 
though  only  in  a  small  degree,  in  islands  situated  within  sight 
of  each  other,  having  the  same  geological  nature,  the  same 
height,  climate,  etc.  ?  This  long  appeared  to  me  a  great  diffi- 
culty: but  it  ai-ises  in  chief  part  from  the  deeply-seated  error 
of  considering  the  physical  conditions  of  a  country  as  the  most 
important ;  whereas  it  cannot  be  disputed  that  the  nature  of 
the  other  inhabitants  with  Avhich  each  has  to  compete  is  at 
least  as  important,  and  generally  a  far  more  important  element 
of  success.  Now,  if  we  look  to  the  species  Avliich  inhabit  the 
Galapagos  Archipelago  and  are  likewise  found  in  other  parts 
of  the  world,  Ave  find  that  they  differ  considerably  in  the  sev- 
eral islands.  This  difference  might  indeed  have  been  expected 
if  the  islands  have  been  stocked  by  occasional  means  of  trans- 
port— a  seed,  for  instance,  of  one  plant  having  been  brought  to 
one  island,  and  that  of  another  plant  to  another  island,  though 
all  proceeding  from  the  same  general  source.  Hence,  when  in 
former  times  an  immigrant  first  settled  on  one  of  the  islands, 
or  when  it  subsequently  spread  from  one  to  another,  it  would 
undoubtedly  be  exposed  to  different  conditions  in  the  different 
islands,  for  it  would  have  to  compete  with  a  different  set  of  or- 
ganisms :  a  plant,  for  instance,  would  find  the  ground  best 
fitted  for  it  occujiied  by  somewhat  different  species  in  the  dif- 
ferent islands,  and  would  be  exposed  to  the  attacks  of  some- 
what dillerent  enemies.  If,  then,  it  varied,  natural  selection 
would  probably  ffivor  different  varieties  in  the  different  islands. 
Some  species,  however,  might  spread  and  yet  retain  the  same 
character  throughout  the  group,  just  as  we  see  some  species 
spreading  widely  throughout  a  continent  and  remaining  the 
same. 

The  really  surprising  fact  in  this  case  of  the  Galapagos 
Archipelago,  and  in  a  lesser  degrcx;  in  some  analogous  cases, 
is,  that  each  new  species,  after  being  formed  in  any  one  island, 
did  not  quickly  spread  to  the  other  islands.  But  the  islands, 
though  in  siglit  of  each  other,  are  se])arated  by  deep  arms  of 
the  sea,  in  most  cases  wider  than  the  Britisli  Channel,  and 
there  is  no  reason   to  suppose  that   they  have  at  any  former 


CiiAi'.  XII.    ISLANDS  TO  THOSE  OF  THE   MAIN-LAND.  2G5 

period  boon  continuously  uuitccL  The  currcuts  of  the  sea  arc 
rapid  and  sweep  across  the  archipela;^o,  and  gales  of  wind  arc 
extraordinarily  rare ;  so  that  the  islands  are  far  more  ciTcct- 
iially  separated  from  each  other  than  they  appear  on  a  map. 
Nevertlieless,  some  of  tlie  species,  both  those  foimd  in  other 
parts  of  tlic  world  and  tliose  confined  to  the  archii)elag-o,  are 
common  to  the  several  islands;  and  we  may  infer  from  their 
present  manner  of  distribution  that  they  have  spread  frona  one 
island  to  the  othei-s.  But  we  often  take,  I  think,  au  erroneous 
view  of  the  probability  of  closely-allied  species  invading  each 
other's  territory,  when  put  into  free  intercommunication.  Un- 
doubtedly, if  one  species  has  any  advantage  over  another,  it 
will  in  a  very  brief  time  wholly  or  in  part  supplant  it ;  but,  if 
both  are  equally  well  fitted  for  their  own  places,  both  proba- 
bly will  hold  their  jilaces  and  keep  separate  for  almost  any 
length  of  time.  Being  familiar  with  the  fact  that  many  spe- 
cies, naturalized  through  man's  agency,  have  spread  with  as- 
tonishing raj)idity  over  wide  areas,  we  are  apt  to  infer  that 
most  species  would  thus  spread ;  but  we  should  remember  that 
the  speci(;s  which  become  naturalized  in  new  countries  are  not 
generally  closely  allied  to  the  aboriginal  inhabitants,  but  are 
very  distinct  forms,  belonging  in  a  large  proportion  of  cases, 
as  shown  by  Alph.  de  CandoUe,  to  distinct  genera.  In  the 
(jrulapagos  Archipelago,  many  even  of  the  birds,  though  so 
well  adapted  for  Hying  from  island  to  island,  are  distinct  on 
each ;  thus  there  are  three  closely-allied  species  of  mocking- 
thrush,  each  confined  to  its  own  island.  Now  let  us  suppose 
the  mocking-thrush  of  Cliatham  Island  to  be  blown  to  Charles 
Island,  which  has  its  own  mocking-thrush ;  why  should  it  suc- 
ceed in  establishing  itself  there  ?  We  may  safely  infer  that 
Charles  Island  is  well  stocked  with  its  own  species,  for  aiuiu- 
ally  more  eggs  are  laid  and  yv>ung  birds  hatched,  than  can 
possibly  be  reared ;  and  we  may  infer  that  the  mocking-tlirush 
l)eculiar  to  Charles  Island  is  at  least  as  well  fitted  for  its  home 
as  is  the  species  pecuhar  to  Chatham  Island.  Sir  C.  Lyell  and 
Mr.  Wollaston  have  communicated  to  me  a  remarkable  fact 
bearing  on  this  subject ;  namely,  that  Madeira  and  the  adjoining 
islet  of  Porto  Santo  possess  many  distinct  but  representative 
species  of  land-shells,  some  of  which  live  in  crevices  of  stone; 
and,  although  large  quantities  of  stone  are  annuallv  transported 
from  Porto  Santo  to  Madeira,  yet  this  latter  island  has  not  be- 
come coloniz(vl  by  the  Porto  Santo  species  :  nevertheless,  both 
islands  have  been  colunized  by  European  land-shells,  which  no 


3G6  KELATIONS  OF  THE  INIIABITAXTS   OF        Ciia.-.  XII. 

doubt  liad  some  advanta<Te  over  tlie  indig-cnous  species.  From 
these  considerations  I  think  wc  need  not  g^reatl}-  marvel  at  the 
endemic  and  representative  species,  Avliicli  inhabit  the  several 
islands  of  tlic  Galapag-os  Archipelago,  not  Laving  universally 
spread  from  island  to  island,  Preoccu])ation  has  also  probably 
played  an  important  part  in  checking  the  connningling  of  the 
species  Avhich  inhabit  different  districts  with  nearly  the  same 
physical  conditions  on  the  same  continent.  Thus,  the  south- 
cast  and  southwest  corners  of  Australia  have  nearly  the  same 
physical  conditions,  and  are  united  by  continuous  land,  yet 
they  are  inhabited  by  a  vast  number  of  distinct  mammals, 
birds,  and  plants. 

The  same  principle  which  governs  the  general  character  of 
the  inhal)itants  of  oceanic  islands,  namely,  their  relation  to  tho 
source  whence  colonists  could  have  been  most  easily  derived, 
together  with  their  subsequent  modification,  is  of  the  widest 
apjilication  throughout  Nature.  We  see  this  on  every  moun- 
tain-summit, in  every  lake  and  marsh.  For  Alpine  species, 
cxcci)ting  in  as  far  as  the  same  species  have  become  widely 
spread  during  the  recent  Glacial  epoch,  are  related  to  those  of 
the  surrounding  lowlands  :  thus  we  have,  in  South  America, 
Aljiine  humming-birds,  Alpine  rodents,  Alpine  plants,  etc.,  all 
strictly  belonging  to  American  forms  ;  and  it  is  obvious  that 
a  mountain,  as  it  liccamo  slowly  upheaved,  Avould  he  colonized 
from  the  surrounding  lowlands.  So  it  is  with  the  inhabitants 
of  lakes  and  marshes,  excepting  in  so  far  that  great  facility  of 
transport  has  allowed  many  of  the  same  species  to  prevail 
through  large  portions  of  the  world.  AVe  see  this  same  prin- 
ciple  in  the  character  of  most  of  the  blind  animals  inhabiting 
the  caves  of  America  and  of  Europe.  Other  analogous  facts 
could  be  given.  It  will,  I  believe,  be  universally  found  true, 
that  wherever  in  two  regions,  let  them  be  ever  so  distant, 
many  closely-allied  or  representative  species  occur,  there  will 
likewise  be  found  some  identical  sjiecies ;  and  wherever  many 
closely-allied  species  occur,  there  Avill  be  found  many  fonns 
wliich  some  naturalists  rank  as  distinct  species,  and  others  as 
mere  varieties ;  these  doubtful  forms  showing  us  the  steps  in 
the  progress  of  modification. 

The  relation  l)etweeu  the  power  and  extent  of  migration  in 
certain  species,  either  at  the  present  or  at  some  fomier  jieriod, 
and  the  existence  at  remote  jioints  of  the  world  of  allied  spe- 
cies, is  shown  in  another  and  more  general  way.  Mr.  Gould 
remarked  to  me  long  ago,  that,  in  those  genera  of  birds  which 


CiiAr.  XII.    ISLANDS  TO  THOSE  OF  THE  MAIN-LAND.  3^7 

range  over  tlic  world,  many  of  the  species  have  very  wide 
rana^es.  I  can  hardly  doubt  that  this  rule  is  generally  true, 
though  it  would  be  difficult  to  prove  it.  Among  mammals,  we 
see  it  strikingly  displayed  in  bats,  and  in  a  lesser  degree  in 
the  Felid;e  and  CanidiV.  We  see  the  same  rule  in  the  distribu- 
tion of  butterflies  and  beetles.  So  it  is  with  most  of  the  in- 
habitants of  fresh  water,  for  many  of  the  genera  in  the  most 
distinct  classes  range  over  the  world,  and  many  of  the  species 
have  enonnous  ranges.  It  is  not  meant  that  all^  but  that  some 
of  the  species  in  the  genera  which  range  very  widely,  have 
themselves  very  wide  ranges.  Nor  is  it  meant  that  the  species 
in  such  genera  have  on  an  average  a  very  wide  range ;  for  this 
will  largely  depend  on  how  far  the  process  of  modilicatiou  has 
gone;  for  instance,  two  varieties  of  the  same  species  inhabit 
America  and  Europe,  and  thus  the  species  has  an  immense 
rjtnge ;  but,  if  variation  were  to  be  carried  a  little  further,  the 
two  varieties  would  be  ranked  as  distinct  species,  and  the 
range  Avould  be  greatly  reduced.  Still  less  is  it  meant,  that 
species  which  have  the  capacity  of  crossing  barriers  and  ranging 
widely,  as  in  the  case  of  certain  powerfullj'-winged  birds,  will 
necessarily  range  widely ;  for  we  should  never  forget  that  to 
range  widely  implies  not  only  the  power  of  crossing  barriers, 
but  the  more  important  power  of  being  ^'ictorious  in  distant 
lands  in  the  struggle  for  life  with  foreign  associates.  But,  ac- 
cording to  the  vi(.'w  that  all  the  species  of  the  same  genus, 
though  now  distributed  at  the  most  remote  points  of  the  worhl, 
are  descended  from  a  single  progenitor,  we  ought  to  find,  and 
I  believe  as  a  general  rule  we  do  find,  that  some  at  least  of  the 
species  range  very  widely. 

We  should  bear  in  mind,  in  relation  to  all  organic  beings, 
that  many  genera  arc  of  very  ancient  origin,  and  the  species  in 
this  case  will  have  had  ample  time  for  dispersal  and  subsequent 
modificati(.)n.  There  is  also  reason  to  believe,  fiom  geological 
evidence,  that  Avithin  each  great  class  the  lower  organisms 
change  at  a  slower  rate  than  the  higher;  consequently  they 
will  liave  had  a  better  chance  of  ranging  widely  and  of  still  re- 
taining the  same  sjjeeific  character.  This  fact,  together  with 
the  seeds  and  eggs  of  almost  all  lowly-organized  forms  l)eing 
very  minute  and  better  fitted  for  distant  transportal,  probably 
accounts  for  a  law  which  has  long  been  observed,  and  which 
has  lately  been  discussed  by  Alpli.  de  CandoUe  in  regard  to 
plants,  namely,  that  the  lower  any  group  of  organisms  stands, 
the  more  widely  it  ranges. 


368  SUM.MAliY   OF  THE  LAST  Chap.  XII. 

The  relations  just  discussed — namely,  lower  oriranisms  ran- 
ging' more  "widely  than  the  higher — some  of  the  species  of  widely- 
ranging  genera  themselves  ranging  widely — such  facts,  as  al- 
l)ine,  lacustrine,  and  marsh  productions  being  generally  related 
to  those  which  live  on  the  surrounding  low-lands  and  drylands 
— the  striking  relationship  between  the  inhabitants  of  islands 
and  tliose  of  the  nearest  main-land — the  still  closer  relationship 
of  the  distinct  inhabitants  of  the  islands  in  the  same  archipelago 
— are  inexplicable  on  the  ordinary  view  of  the  independent 
creation  of  each  species,  l)ut  arc  explicable  if  we  admit  coloni- 
zation from  the  nearest  or  readiest  source,  together  with  the 
subsequent  adaptation  of  the  colonists  to  their  new  homes. 

Summary  of  the  last  and 2)^'c^C}it  Chapter. 

In  these  chapters  I  have  endeavored  to  show  that,  if  we 
make  due  allowance  for  our  ignorance  of  the  full  effects  of  the 
changes  of  climate  and  of  the  level  of  the  land,  which  have  cer- 
tainly occurred  within  the  recent  period,  and  of  other  changes 
which  have  probably  occurred — if  Ave  remember  how  ignorant 
M'e  are  with  respect  to  the  many  curious  means  of  occasional 
transport — if  we  bear  in  mind  how  often  a  species  may  have 
ranged  continuously  over  a  wide  area,  and  then  have  become 
extinct  in  the  intermediate  tracts — the  difficulty  is  not  insuper- 
able in  believing  that  all  the  individuals  of  the  same  species, 
wherever  found,  are  descended  from  common  parents.  And 
we  are  led  to  this  conclusion,  which  has  been  arrived  at  by 
many  naturalists  under  the  designation  of  single  centres  of 
creation,  by  various  general  considerations,  more  especially 
from  the  importance  of  barriers  of  all  kinds,  and  from  the  ana- 
logical distribution  of  sub-genera,  genera,  and  families. 

With  respect  to  distinct  species  belonging  to  the  same 
genus,  Avhich  on  our  theory  must  have  spread  from  one  parent- 
source  ;  if  Ave  make  the  same  allowance  as  before  for  our  igno- 
rance, and  remember  that  some  forms  of  life  have  changed  A'cry 
slowly,  enormous  periods  of  time  having  been  thus  granted  for 
tlieir  migration,  the  difficulties  are  far  from  insuperable;  though 
in  this  case,  and  in  that  of  the  individuals  of  the  same  species, 
they  are  often  great. 

As  exemplifying  the  effects  of  climatal  changes  on  distribu- 
tion, I  liaA'c  attempted  to  shoAV  how  important  a  part  the  Gla- 
cial period  has  played,  Avhich  affected  even  the  equatorial 
regions,  and  Avhich,  during  the  alternations  of  the  cold  in  the 


Chap.  XII.  AND  TKESENT  CHAPTER.  3(J9 

north  and  soutli,  allowed  the  productions  of  ojipositc  hemi- 
spheres to  mingle,  and  left  some  of  them  stranded  in  all  parts 
of  the  world  on  the  mountain-summits.  As  showing  how  diver- 
sified are  the  means  of  occasional  transport,  I  have  discussed 
at  some  little  length  the  means  of  dispersal  of  fresh-water  pro- 
ductions. 

If  the  difliculties  be  not  insuperable  in  admitting  that  in 
the  long  course  of  time  all  the  individuals  of  the  same  species, 
and  likewise  of  the  several  species  belonging  to  the  same  ge- 
nus, have  proceeded  from  some  one  source  ;  then  all  the  grand 
leading  facts  of  geographical  distribution  are  explicable  on  the 
theory  of  mioTation,  together  with  subsetiuent  modification  and 
the  multiplication  of  new  forms.  We  can  thus  understand  the 
high  imixtrtancc  of  barriers,  whether  of  land  or  water,  in  not 
only  s{'j)arating,  but  in  apparently  forming  the  several  zoologi- 
cal and  botanical  provinces.  We  can  thus  understand  the 
concentration  of  related  species  within  the  same  areas;  and 
how  it  is  that  under  different  latitudes,  for  instance  in  South 
America,  the  inliabitants  of  the  i>lains  and  mountains,  of  the 
forests,  marshes,  and  deserts,  are  linked  together  in  so  mysteri- 
ous a  manner,  and  are  likewise  linked  to  the  extinct  beings 
which  fonnerly  inhabited  the  same  continent.  Bearing  in  mind 
that  the  mutual  relation  of  organism  to  organism  is  of  the  high- 
est importance,  we  can  see  why  two  areas  liaving  nearly  the 
same  phj'sical  conditions  sliould  often  be  inhabited  by  very 
different  forms  of  life ;  for,  according  to  the  length  of  time 
which  has  elapsed  since  the  colonists  entered  one  of  the  regions, 
or  both;  according  to  the  nature  of  the  communication  which 
allowed  certain  forms  and  not  others  to  enter,  either  in  greater 
or  lesser  numbers;  according  or  not  as  those  which  entered 
happened  to  come  into  more  or  less  direct  coinpetiti(m  with 
each  other  and  with  the  aborigines  ;  and  according  as  the  im- 
migrants were  capable  of  varying  more  or  less  rapidly,  there 
would  ensue  in  the  two  or  more  regions,  indejiendently  of  their 
phj-sical  conditions,  infinitcly-diver.sified  conditions  of  life  — 
there  would  be  an  almost  endless  amount  of  organic  action  and 
reaction — and  we  should  lind,  as  we. do  find,  some  groups  of 
beings  greatly,  and  some  only  slightly,  modified — some  devel- 
oped in  great  force,  some  existing  in  scanty  numbers — in  the 
several  great  geographical  provinces  of  the  world. 

On  these  same  principles  we  can  undc^rstand,  as  I  have  en- 
deavored to  show,  why  oceanic  islands  should  have  few  in- 
habitants, but  of  these  a  great  number  should  be  endemic  or 


370  SUMMAKY  OF  THE  LAST  Ciiai-.  XII. 

peculiar;  aii<l  'wliy,  in  rclalion  to  tlie  means  of  iiii<>ration,  one 
group  of  beings,  even  Avithin  the  same  class,  should  have  all  its 
species  peculiar,  and  another  group  should  have  all  its  species 
the  same  Avith  those  in  other  quarters  of  the  world.  We  can 
see  why  "whole  groups  of  organisms,  as  batrachians  and  terres- 
trial mammals,  should  be  absent  from  oceanic  islands,  Avhilc  the 
most  isolated  islands  should  possess  their  own  peculiar  species 
of  aerial  mammals  or  bats.  We  can  see  why  there  should  be 
some  relation  between  the  presence,  in  islands,  of  mammals,  in 
a  more  or  less  modified  condition,  and  the  depth  of  the  sea  be- 
tween such  islands  and  the  main-land.  We  can  clearly  see  why 
all  the  inhabitants  of  an  archipelag-o,  though  specifically  distinct 
on  the  several  islets,  should  be  closely  related  to  each  other, 
and  likewise  be  related,  but  less  closely,  to  those  of  the  nearest 
ccnitinent  or  other  source  whence  immigrants  might  have  been 
derived.  AVe  can  sec  why,  in  two  areas,  however  distant  from 
each  other,  where  very  closely-allied  or  representative  species 
exist,  there  should  almost  always  exist  some  identical  species. 
As  the  late  Edward  Forbes  often  insisted,  there  is  a  striking 
parallelism  in  the  laws  of  life  throughout  time  and  space:  the 
laws  governing  the  successioni  of  fonns  in  past  times  being 
nearly  the  same  with  those  governing  at  the  present  time  the 
differences  in  difTerent  areas.  We  see  this  in  many  facts,  llie 
endurance  of  each  species  and  group  of  species  is  continuous  in 
time ;  for  the  exceptions  to  the  rule  are  so  few,  that  they  may 
be  fairly  attributed  to  our  not  having  as  yet  discovered  in  an 
intermediate  dei")Osit  certain  forms  which  are  absent  in  it,  but 
which  occur  both  above  and  below :  so  in  space,  it  certainly  is 
the  general  rule  that  the  area  inhabited  by  a  single  species,  or 
by  a  grouji  of  species,  is  continuous,  and  the  exceptions,  which 
are  not  rare,  may,  as  I  have  attempted  to  show,  be  accounted 
for  by  former  migrations  mider  difTerent  circumstances,  or 
through  occasional  means  of  transport,  or  by  the  species  having 
become  extinct  in  the  intermediate  tracts.  Both  in  time  and 
space,  species  and  groups  of  species  have  their  points  of  maxi- 
mum development.  Groups  of  species,  living  during  the  same 
j)eri(jd  of  time,  or  living  jvitliin  the  same  area,  are  often  char- 
acterized by  trifling  features  in  common,  as  of  sculpture  or 
color.  In  looking  to  the  long  succession  of  past  ages,  as  in 
now  looking  to  distant  provinces  throughout  the  world,  we 
find  that  species  in  certain  classes  differ  little  from  each  other, 
while  others  in  a  different  class,  or  only  in  a  different  family  of 
the  same  order,  differ  greatly  from  each  other.     In  both  time 


CiiAP.  XII.  AND   PRESENT  CHAPTER.  37I 

and  space  the  lowly-orn^auized  members  of  each  class  generally 
change  less  than  the  highly-organized ;  but  there  are  in  botli 
cases  marked  exceptions  to  the  rule.  According  to  our  theory 
these  several  relations  throughout  time  and  space  arc  intelli- 
gible ;  for,  whether  we  look  to  the  forms  of  life  which  have 
changed  during  successive  ages,  or  to  those  which  have  changed 
after  having  migrated  into  distant  quarters,  in  both  cases  the 
forms  witliin  each  class  arc  connected  by  the  same  bond  of  or- 
dinary generation  ;  and  in  both  cases  the  laws  of  variation  have 
been  the  same,  and  modifications  have  been  accumulated  by 
the  same  means  of  natural  selection. 


37S  CLASSIFICATION.  Cuap.  XIII. 


CHAPTER   XIII. 

MUTUAL    AFFINITIES    OF    ORGANIC   BEINGS:    MOEPHOLOGY :    EM- 
BRYOLOGY:   RUDIMENTARY    ORGANS. 

Classifiriition.  Groups  subordinate  fn  Group? — Natural  System— Rnlcs  ;ind  Difficiiltica 
in  Chissilio.'UiDii.  explained  on  tlio  Theory  of  Descent  with  Moditicalion — Classi- 
fication of  Vnrieliew— Descent  alwavH  used  in  Classification — Analofrical  or  Adap- 
tive Characters — Affinities,  General.  Complex,  and  liadiatincj— Extinction  sepa- 
rates and  defines  Groups — Morpliolou'V-  between  members  of  the  same  Class,  be- 
tween parts  of  the  same  Individual — Embryoloiry.  Laws  of.  explained  by  Vari.i- 
tions  not  supervening  at  an  early  Age,  and  being  inherited  at  a  corresponding 
Age — Kudimeutary  Organs  ;  their  Origin  explainuU — Suinniar3'. 

Classijtcation. 

From  a  very  remote  period  in  the  history  of  the  world  or- 
ganic beings  have  resembled  each  other  iu  descending  degrees, 
so  that  they  can  be  classed  in  groups  under  groups,  litis 
classiftcation  is  not  arbitrary,  like  the  grouping  of  the  stars  in 
constellations.  The  existence  of  groups  would  have  been  of 
simple  signification,  if  one  group  had  been  exclusively  fitted  to 
inhtibit  the  land,  and  another  tlie  water;  one  to  feed  on  flesh, 
another  on  vegetable  matter,  and  so  on  ;  but  the  case  is  widely 
different  in  Nature  ;  for  it  is  notorious  how  commonly  members 
of  even  the  same  sub-group  have  dilfercnt  habits.  In  the  second 
:ind  fourth  chapters,  on  Variation  and  on  Natural  Selection,  I 
have  attempted  to  show  that  within  each  country  it  is  the 
Avidel^'-ranging,  the  much-dilfused  and  common,  that  is,  the 
dominant  sj^ccies  belonging  to  the  larger  genera  in  each  class, 
which  vary  most.  The  varieties,  or  incipient  species,  thus  pro- 
duced, ultimately  become  converted  into  new  and  distinct  spe- 
cies ;  and  these,  on  the  principle  of  inheritance,  tend  to  pro 
duce  other  new  and  dominant  species.  Consequently,  the 
groups  which  are  now  large,  and  which  generally  include  many 
dominant  sjiecies,  tend  to  go  on  increasing  in  size.  I  further 
attempted  to  show  that,  from  the  varying  descendants  of  each 
species  t  tying  to  occupy  as  many  and  as  different  places  as  pos- 


Chap.  XIII.  CLASSIFICATION.  373 

siblc  in  the  economy  of  Nature,  there  is  a  constant  tendency  in 
their  characters  to  diverge.  This  latter  conclusion  is  supported 
by  observing  tlio  great  diversity  of  forms  which  in  any  small 
area  come  into  the  closest  competition,  and  by  certain  facts  in 
naturalization. 

I  attempted  also  to  show  that  there  is  a  constant  tendency 
in  the  forms  -which  arc  increasing  in  number  and  diverging  in 
character,  to  supplant  and  exterminate  the  preceding,  less 
divergent  and  less  improved  forms.  I  request  the  reader  to 
turn  to  the  diagram  illustrating  the  action,  as  formerly  ex- 
])lained,  of  these  several  jmnciples ;  and  he  will  see  that  the 
inevitable  result  is,  that  tlie  modilied  descendants  proceeding 
from  one  progenitor  become  broken  up  into  groups  subordi- 
nate to  groups.  In  the  diagram  each  letter  on  the  uppermost 
line  may  represent  a  genus  including  sevei'al  species ;  and  the 
whole  of  tlie  genera  along  this  upper  line  form  together  one 
class,  for  all  arc  descended  from  one  ancient  parent,  and,  con- 
sequentl}',  have  inherited  something  in  common.  But  the 
three  genera  on  the  left  hand  have,  on  this  same  principle, 
nnich  in  common,  and  form  a  sul>family,  distinct  from  that  in- 
cluding the  next  two  genera  on  the  right  hand,  w^hich  diverged 
from  a  common  parent  at  the  fifth  stage  of  descent.  These 
five  genera  have  also  much,  though  less,  in  common ;  and  they 
form  a  faniilv  distinct  from  that  including  the  three  genera  still 
fartlier  to  tlie  right  liand,  which  diverged  at  a  still  earlier 
period.  And  all  these  genera,  descended  from  (A),  form  an 
order  distinct  from  the  genera  descended  from  (1).  So  tliat 
we  here  have  many  species  descended  from  a  single  progenitor 
groujied  into  genera ;  and  the  genera  in  sub-families,  families, 
and  orders,  all  in  one  great  class.  Thus,  the  grand  fact  of  the 
natural  suliordination  of  all  organic  beings  in  groups  under 
groups,  which,  from  its  familiarity^,  does  not  always  sulliciently 
strike  us,  is  in  my  judgment  explained.  No  doubt  organic 
lieings,  like  all  other  objects,  can  be  classed  in  many  ways, 
either  artificially  by  single  characters  or  more  naturally  by  a 
number  of  characters.  We  know,  for  instance,  that  minerals 
and  the  elemental  substances  can  be  thus  aiTanged  ;  in  this 
case  there  is  of  course  no  relation  to  genealogical  succession, 
and  no  cause  can  at  present  be  assigned  for  tlicir  falling  into 
group.s.  But  with  organic  beings  the  case  is  different,  and  the 
view  above  given  explains  their  natural  an-angement  in  group 
under  gr(jup ;  and  no  other  explanation  has  ever  hccn  at- 
tcm])lc(l. 


r,74  CLASSIFICATION.  Chap.  XIII 

Naturalists,  as  we  have  seen,  try  to  arraiioc  the  species, 
genera,  and  families  in  each  class,  on  what  is  called  the  Natu- 
ral System.  But  -what  is  meant  by  this  system  ?  Some 
authors  look  at  it  merely  as  a  scheme  for  arranginj^  tog'ethcr 
those  llvina^  objects  which  are  most  alike,  and  for  separating 
those  which  are  most  inilike  ;  or  as  an  artificial  means  for 
enunciating,  as  briefly  as  possible,  general  propositions — that 
is,  by  one  sentence  to  give  the  characters  common,  for  instance, 
to  all  mammals,  by  another  those  common  to  all  carnivora,  by 
another  those  conunon  to  the  dog-genus,  and  then,  by  adding 
a  single  sentence,  a  full  description  is  given  of  each  kind  of 
dog.  The  ingenuity  and  utility  of  this  system  are  indispu- 
table. But  many  naturalists  think  that  something  more  is 
meant  ])y  the  Natural  System  ;  they  believe  that  it  reveals  the 
plan  of  the  Creator ;  but,  unless  it  be  specified  Avhether  order 
in  time  or  space,  or  both,  or  what  else  is  meant  by  the  plan 
of  the  Creator,  it  seems  to  me  that  nothing  is  thus  added  to 
our  knowledge.  Such  expressions  as  that  fiimous  one  by  Lin- 
nieus,  and  which  wc  often  meet  with  in  a  more  or  less  con- 
cealed form,  that  the  characters  do  not  make  the  genus,  but 
that  the  genus  gives  the  characters,  seem  to  imply  that  some- 
thing more  is  included  in  our  classification  than  mere  resem- 
blance. I  believe  that  something  more  is  included,  and  that 
propin(juity  of  descent — the  only  known  cause  of  the  similarity 
of  organic  beings — is  the  bond,  hidden  as  it  is  by  various  de- 
grees of  modification,  which  is  partially  revealed  to  us  by  our 
classifications. 

Let  us  now  consider  the  rules  followed  in  classification, 
and  the  difficulties  which  are  encountered,  on  the  view  that 
classification  either  gives  some  imknown  plan  of  creation,  or  is 
simply  a  scheme  for  enunciating  general  propositions  and  of 
jilacing  together  the  forms  most  like  each  other.  It  might 
have  been  thought  (and  Avas  in  ancient  times  thought)  that 
those  parts  of  the  structure  which  determined  the  habits  of  life, 
and  the  general  place  of  each  being  in  the  economy  of  Nature, 
would  be  of  very  high  importance  in  classification.  Nothing 
can  be  more  false.  No  one  regards  the  external  similarity  of  a 
mouse  to  a  shrew,  of  a  dugong  to  a  whale,  of  a  whale  to  a  fish, 
as  of  any  importance.  These  reseml)lances,  though  so  intimate- 
ly connected  with  the  whole  life  of  the  being,  are  ranked  as 
merely  "  adaptive  or  analogical  characters  ; "  but  to  the  con- 
sideration of  these  resemblances  we  shall  recur.  It  may  even 
be  given  as  a  general  rul(>,  that  the  less  nny  part  of  the  organi- 


CriAr.  XIII.  CLASSIFICATION.  375 

zation  is  concerned  with  special  habits,  the  more  important  it 
becomes  for  chissilication.  As  an  instance — Owen,  in  speak- 
inf];'  of  the  dufjonp:,  says  :  "  The  generative  or<^ans,  Ijein^r  those 
wiiich  are  most  remotely  related  to  the  habits  and  food  of  an 
animal,  I  have  always  regarded  as  alTordinti;  very  clear  indica- 
tions of  its  true  airmities.  We  are  least  likely  in  the  modifi- 
cations of  these  organs  to  mistake  a  merely  adaptive  for  an 
essential  character."  With  plants,  how  remarkable  it  is  that 
the  organs  of  vegetation,  on  which  tlieir  nutrition  and  life  de- 
]icnd,  are  of  little  signification  ;  whereas  the  organs  of  repro- 
duction, with  their  product  tlie  seed  and  embr^'o,  are  of  ])ara- 
mount  importance  !  So,  again,  in  formerly  discussing  morpho- 
logical dilleronces  M'hich  are  not  jihysiologically  important,  we 
have  seen  that  they  are  often  of  the  highest  service  in  classifi- 
cation. Tliis  depends  on  their  constancy  througliout  many 
allied  groups  ;  and  the  constancy  depends  chiefly  on  any  shght 
deviations  of  structure  in  such  parts  not  having  been  pre- 
served and  accumulated  by  natural  selection,  wliich  acts  only 
on  useful  characters. 

That  tlie  mere  jihysiological  importance  of  an  organ  does 
not  determine  its  classificatory  value,  is  almost  proved  by  the 
fact  that  in  allied  groups,  in  which  the  same  organ,  as  w^e  have 
every  reason  to  suppose,  has  nearly  the  same  physiologi- 
cal value,  its  classificatory  value  is  widely  difltM-ent.  No 
naturalist  can  have  worked  at  aily  group  without  being  struck 
with  this  fact ;  and  it  has  been  fully  acknowledged  in  the 
writings  of  almost  every  author.  It  will  suffice  to  quote  the 
highest  aulhorily,  Kobert  ]}ro'\\Ti,  who,  in  speaking  of  certain 
organs  in  the  Proteacere,  says,  their  generic  importance,  "  like 
that  of  all  their  parts,  not  only  in  this,  Init,  as  I  apprehend,  in 
every  natural  familv,  is  verv  unequal,  and  in  some  cases  seems 
to  be  entirely  lost."  Again,  in  another  work,  he  says,  the 
genera  of  the  Connaracea?  "  differ  in  having  one  or  more 
ovaria,  in  the  existence  or  absence  of  albumen,  in  the  imbri- 
cate or  valvular  rcstivation.  Any  one  of  these  characters 
singly  is  fref|uently  of  more  than  generic  importance,  though 
here  even  when  all  taken  together  they  a])pear  insufficient 
to  separate  Cnestis  from  Connarus."  To  give  an  example 
among  insects:  in  one  great  division  of  the  Ilymenoptera, 
the  antenna?,  as  Westwood  has  remarked,  arc  most  constant 
in  structure  ;  in  another  division  they  differ  nuich,  and  the 
differences  are  of  (juitc  subordinate  vahie  in  classification  ;  yet 
no  one  will  say  that  the  antennif  in  these  two  divisions  of  the 


37G  CLASSIFICATION.  CriAr.  XIII. 

same  order  are  of  unequal  jilijsiological  importance.  Any 
number  of  instances  could  be  given  of  the  varying  importance 
for  classification  of  the  same  important  organ  williin  the  same 
group  of  beings. 

Agahi,  no  one  Avill  say  that  rudimentary  or  atrophied  or- 
gans are  of  high  physiological  or  ^ital  importance ;  ^-et,  un- 
doubtedly, organs  in  this  condition  are  often  of  high  value  in 
classification.  No  one  will  dispute  that  the  rudimentary  teeth 
in  the  upper  jaws  of  young  ruminants,  and  certain  rudimentary 
bones  of  the  leg,  are  highly  serviceable  in  exhibiting  the  close 
affinity  between  Ruminants  and  Pachyderms.  Robert  Brown 
has  strongly  insisted  on  the  fact  that  the  position  of  the  rudi- 
mentary florets  is  of  the  highest  importance  in  the  classification 
of  the  Grasses. 

Numerous  instances  could  be  given  of  characters  derived 
Ij-om  parts  which  must  be  considered  of  Acry  trifling  physiolo- 
gical importance,  but  which  are  universally  admitted  as  highly 
serviceable  in  the  definition  of  Avhole  groups.  For  instance, 
whether  or  not  there  is  an  open  passage  from  the  nostrils  to 
the  mouth,  the  only  character,  according  to  Owen,  which  abso- 
lutely disting-uishcs  fishes  and  reptiles — the  inflection  of  the 
angle  of  the  jaws  in  ^larsupials — the  manner  in  which  the 
wings  of  insects  are  folded — mere  color  in  certain  Alga; — mere 
pubescence  on  parts  of  the  tlower  in  grasses — the  nature  of 
the  dermal  covering,  as  hair  or  feathers,  in  the  Vertebrata. 
If  the  Ornithorhyncluis  had  been  covered  with  feathers  instead 
of  hair,  this  external  and  trifling  character  would  have  been 
considered  by  naturalists  as  an  important  aid  in  determining 
the  degree  of  affinity  of  this  strange  creature  to  birds. 

The  importance,  for  classilication,  of  trifling  characters, 
mainly  depends  on  their  being  correlated  Avith  several  other 
characters  of  more  or  less  importance.  The  value  indeed  of  an 
aggregate  of  characters  is  very  evident  in  natural  history. 
Hence,  as  has  often  been  remarked,  a  species  may  depart  from 
its  allies  in  several  characters,  both  of  high  physiological  im- 
portance and  of  almost  universal  prevalence,  and  A'ct  leave  us 
in  no  doubt  where  it  sliould  be  ranked.  Hence,  also,  it  has 
been  found  that  a  classification  founded  on  any  single  charac- 
ter, however  important  that  may  be,  has  always  failed ;  for  no 
part  of  the  organization  is  invariably  constant.  The  impor- 
tance of  an  aggregate  of  characters,  even  when  none  are  im- 
portant, alone  explains  the  aphorism  by  Linuiens,  naTuely,  that 
the  characters  do  not  give  the  genus,  but  the  genus  gives  the 


CiiAP.  .\III.  CLASSIFICATION.  377 

characters  ;  for  this  seems  foun  Jed  on  an  .appreciation  of  many 
trillinp;'  points  of  resemblance,  too  slif^ht  to  be  delinetl.  Cer- 
tain plants,  belongiiii^  to  the  Mali)igliiacene,  bear  perfect  and 
degraded  fio\vcrs;  in  the  hitter,  as  A.  do  Jussicuhas  remarked, 
"  the  grc'iter  nuinl)er  of  the  characters  proper  to  the  species, 
to  the  genus,  to  tlie  family,  to  the  class,  disappear,  and  thus 
laugh  at  our  classification."  But  when  Aspicarpa  produced  in 
France,  during  several  years,  only  degraded  flowers,  departing 
so  wonderfully  in  a  number  of  the  most  important  points  of 
structure  from  the  proper  type  of  the  order,  yet  M.  Richard 
sagaciously  saw,  as  Jussieu  observes,  that  this  genus  should 
still  be  retained  among  the  MalpighiacefO.  This  case  seems  to 
me  well  to  illustrate  the  spirit  of  our  classification. 

Practically,  Avhen  naturalists  are  at  work,  they  do  not 
trouble  themselves  about  the  physiological  value  of  the  charac- 
ters which  they  use  in  defining  a  group  or  in  allocating  any 
particular  species.  If  they  find  a  character  nearly  uniform,  and 
common  to  a  great  number  of  forms,  and  not  common  to 
others,  they  use  it  as  one  of  high  value  ;  if  common  to  some 
lesser  number,  they  use  it  as  of  subordinate  value.  This  prin- 
ciple has  been  broadly  confessed  by  some  naturalists  to  be  the 
true  one;  and  by  none  more  clearly  than  by  that  excellent 
botanist,  Aug.  St.  Hilaire.  If  certain  characters  are  always 
found  correlated  with  others,  though  no  apparent  bond  of  con- 
nection can  be  discovered  between  them,  especial  value  is  set 
on  them.  As  in  most  groups  of  animals,  important  organs, 
such  as  those  fc^r  propelling  the  blood,  or  for  aerating  it,  or 
those  for  propagating  the  race,  arc  foimd  nearly  uniform,  they 
are  considered  as  highly  sernceable  in  classification;  but  in 
some  groups  of  anim:ds  all  these,  the  most  important  vital 
organs,  are  found  to  ofler  characters  of  quite  subordinate  value. 
Thus,  as  Fritz  MllUer  has  lately  remarked,  in  the  same  group 
of  crustaceans,  ('ypridina  is  furnished  Avith  a  heart,  while  in 
two  closely-allied  genera,  namely,  C^-pris  and  Cytherea,  there 
is  no  such  organ  :  one  species  of  Cypridina  has  well-developed 
branchi.'C,  while  another  species  is  destitute  of  them. 

Wo  can  see  why  characters  derived  from  the  embrj^o  should 
be  of  equal  importance  with  those  derived  from  the  adult,  for 
a  natural  classification  of  course  includes  all  ages.  But  it  is 
by  no  means  ol)vious,  on  the  ordinary  view,  why  the  structure 
of  the  embryo  should  be  more  important  for  this  purpose  than 
that  of  the  adult,  which  alone  plays  its  full  part  in  the  econo- 
my of  Nature.     Yet  it  has  been  strongly  urged  by  those  great 


378  CLASSIFICATION.  Chap.  XIII. 

naturalists,  iMiliic  Edwards  and  Ag'assiz,  tliat  embryoloijifal 
characters  ai  o  the  most  important  of  all ;  and  this  doctrhie  has 
very  g'encrally  been  admitted  as  true.  Nevertheless,  their  im- 
portaTicc  has  sometimes  been  exaggerated;  in  order  to  show 
tlii.s,  Fritz  Miillcr  arranged  by  the  aid  of  such  characters  the 
great  class  of  crustaceans,  and  the  arrangement  did  not  prove 
a  natural  one.  But  there  can  be  no  douljt  that  characters  de- 
rived from  tlie  embryo  are  generally  of  the  highest  value,  not 
only  Avith  animals  but  Avith  plants.  Thus  the  two  main  divis- 
ions of  flowering  plants  are  founded  on  differences  in  the  em- 
bryo— on  the  number  and  position  of  the  cotyledons,  and  on 
the  mode  of  development  of  the  plumule  and  radicle.  Wc 
shall  immediately  see  why  these  characters  possess  so  high  a 
value  in  classification,  namely,  from  the  natural  system  being 
genealogical  in  its  arrangement. 

Our  classifications  are  often  plainly  influenced  by  chains  of 
aflinities.  Nothing  can  be  easier  than  to  define  a  number  of 
chanicters  common  to  all  birds  ;  but  in  the  case  of  crustaceans, 
such  definition  has  hitherto  been  found  impossible.  There  are 
crustaceans  at  the  opposite  ends  of  the  series,  which  have 
hardly  a  character  in  common ;  yet  the  species  at  both  ends, 
from  being  plainly  allied  to  others,  and  these  to  others,  and 
so  onward,  can  be  recognized  as  unequivocally  belonging  to 
this,  and  to  no  other  class  of  the  Articulata. 

Geographical  distribution  has  often  been  used,  though  per- 
haps not  quite  logically,  in  classification,  more  especially  in 
very  largo  groups  of  closely-allied  forms.  Temminck  insists 
on  the  utility  or  even  necessity  of  this  practice  in  certain 
groups  of  birds ;  and  it  has  been  followed  by  several  entomol- 
ogists and  botanists. 

Finally,  wutli  respect  to  the  comparative  value  of  the  vari- 
ous groups  of  species,  such  as  orders,  sub-orders,  families,  sub- 
families, and  genera,  they  seem  to  be,  at  least  at  present, 
almost  arbitrary.  Several  of  the  best  botanists,  such  as  Mr. 
IJontham  and  others,  have  strongly  insisted  on  their  arbitrary 
value.  Instances  could  be  given  among  plants  and  insects,  of 
:i  group  of  forms,  first  ranked  by  ])ractised  naturalists  as  only 
a  genus,  and  then  raised  to  the  rank  of  a  sub-family  or  family ; 
and  this  has  been  done,  not  because  further  research  has  de- 
tected important  structural  differences,  at  first  overlooked,  but 
because  nmnerous  allied  species,  with  slightly-different  grades 
of  difference,  have  been  subsequently  discovered. 

All  the  foregoing  rules  and  aids  and  difBcultics  in  classifi- 


Chap.  XIII.  CLASSIFICATION.  3-79 

cation  arc  explained,  if  I  do  not  greatly  deceive  myself,  on  the 
view  that  the  Natural  System  is  founded  on  descent  Avitli 
modification;  that  the  characters  which  naturalists  consider  as 
showing  true  allinity  between  any  two  or  more  species,  are 
those  which  have  been  inherited  from  a  connnon  parent,  all  true 
classification  being  genealogical ;  that  community  of  descent 
is  the  hidden  bond  Avhich  naturalists  have  been  unconsciously 
seeking,  and  not  some  unknown  plan  of  creation,  or  the  enun- 
ciation of  general  propositions,  and  the  mere  putting  together 
and  separating  objects  more  or  less  alike. 

But  I  must  explain  my  meaning  more  fully.  I  believe  that 
the  arret)} rjcment  of  the  groujis  within  each  class,  in  due  sub- 
ordination and  relation  to  each  other,  must  be  strictly  genea- 
logical in  order  to  be  natural ;  but  that  the  amount  of  diflerence 
in  the  several  branches  or  groups,  though  allied  in  the  same 
(h'grce  in  blood  to  their  common  progenitor,  may  diller  greatly, 
In'ing  duo  to  the  different  degrees  of  modification  Avhich  they 
have  luidergone ;  and  this  is  expressed  by  the  forms  being 
ranked  under  different  genera,  families,  sections,  or  orders. 
The  reader  will  best  understand  what  is  meant,  if  he  will  take 
the  trouble  to  refer  to  the  diagram  in  the  fourth  chapter.  We 
will  sup]iose  the  letters  A  to  L  to  rcpi'csent  during  the  Silurian 
epoch  allied  genera,  descended  from  some  still  earlier  forms. 
In  three  of  these  genera  (A,  F,  and  I)  the  species  have  trans- 
mitted modified  descendants  to  the  present  day,  represented  l)y 
the  fifteen  genera  («'*  to  s'*)  on  the  uppermost  horizontal  line. 
Now  all  these  modified  descendants  from  a  single  species,  are 
related  in  blood  or  descent  to  the  same  degree ;  they  may 
metaphorically  be  called  cousins  to  the  same  millionth  degTce  ; 
y(}t  tiiey  differ  widely  and  in  diU'ercnt  degrees  from  each  other. 
The  forms  descended  from  A,  now  broken  up  into  two  or  three 
families,  constitute  a  distinct  order  from  those  descended  from 
I,  also  broken  up  into  two  families.  Nor  can  the  existing  sjie- 
cies,  desecnded  from  A,  be  ranked  in  the  same  genus  with  the 
parent  A;  or  those  from  I,  with  the  parent  I.  But  the  exist- 
ing geiuis  f"  may  be  supposed  to  have  been  but  slightly  modi- 
tied  ;  and  it  will  then  rank  with  tlie  parent-genus  F ;  just  as 
some  few  still  living  organisms  belong  to  Silurian  genera.  So 
Ihat  the  amount  or  value  of  the  differences  between  these  or- 
ganic beings  which  arc  all  related  to  each  other  in  the  same 
degree  in  blood,  has  come  to  be  widely  different.  Nevertheless, 
their  genealogi(Ml  arranffcment  remains  strictly  true,  not  only 
at  tlie  present  time,  but  at  each  successive  period  of  descent. 


380  CLASSIFICATION.  Cnxr.  XIII. 

All  the  modified  descendants  from  A  will  have  inherited  some- 
thing' in  common  from  their  common  parent,  as  will  all  the  de- 
scendants from  I ;  so  will  it  be  with  each  subordinate  branch  of 
descendants,  at  each  successive  stage.  If,  however,  we  suppose 
any  descendant  of  A  or  of  I  to  have  been  so  much  modified  as 
to  have  lost  all  traces  of  its  parentage,  in  this  case,  its  place  in 
the  natural  system  will  likev>dse  be  lost — as  seems  to  have  oc- 
curred with  some  few  existing  organisms.  All  the  descendants 
of  the  genus  F,  along  its  whole  line  of  descent,'  are  supposed 
to  have  been  but  little  modified,  and  they  form  a  single  genus 
But  this  genus,  tliough  much  isolated,  will  stiil  occupy  its  projv 
er  intermediate  position.  This  natural  arrangement  is  shown 
in  the  diagram  as  far  as  is  possible  on  paper,  but  in  much  too 
simple  a  manner.  If  a  branching  diagram  had  not  been  used, 
and  only  the  names  of  the  groups  had  been  written  in  a  linear 
series,  it  would  have  been  still  less  possible  to  have  given  a 
natural  arrangement ;  and  it  is  notoriously  not  possible  to  rep- 
resent in  a  series,  on  a  flat  surface,  tlic  aflinities  which  we  dis- 
cover in  Nature  among  the  beings  of  the  same  group.  Thus, 
on  the  view  which  I  hold,  the  natural  system  is  genealogical 
in  its  arrangement,  like  a  i^edigrcc ;  but  the  amount  of  modifi- 
cation which  the  different  groups  have  undergone  has  to  be 
expressed  by  ranking  them  und(?r  different  so-called  genera, 
sub-families,  families,  sections,  orders,  and  classes. 

It  may  be  worth  while  to  illustrate  this  view  of  classification, 
by  taking  the  case  of  languages.  If  we  possessed  a  perfect 
jiedigree  of  mankind,  a  genealogical  arrangement  of  the  races 
of  man  would  afford  the  best  classification  of  the  various  lan- 
guages now  spoken  throughout  the  world  ;  and  if  all  extinct  lan- 
guages, and  all  intermediate  and  slowly-changing  dialects,  had 
to  be  included,  such  an  arrangement  would  be  the  only  pos- 
sible one.  Yet  it  might  be  that  some  ancient  languages  had 
altered  very  little  and  had  given  rise  to  few  new  languages, 
while  others  had  altered  much,  o\\'ing  to  the  spreading,  isola- 
tion, and  state  of  civilization  of  the  several  co-descended  races, 
and  liad  thus  given  rise  to  many  new  dialects  and  languages. 
The  various  degrees  of  difference  between  the  languages  of 
tlie  same  stock  would  have  to  be  expressed  by  groups  subordi- 
nate to  groups  ;  but  the  proper  or  even  only  possible  arrange- 
ment would  still  be  genealogical ;  and  this  would  be  strictly 
natimal,  as  it  would  connect  together  all  languages,  extinct  and 
recent,  by  the  closest  affmitics,  and  would  give  the  filiation  and 
origin  of  each  tongue. 


Chap.  XIII.  CLASSIFICATION.  381 

In  confirmation  of  this  view,  let  us  glance  at  the  classifica- 
tion of  varieties,  which  are  believed  or  known  to  be  descended 
i'roin  a  sinu:le  sjiecies.  These  are  grouped  under  the  species, 
witli  the  sub-variclies  under  the  varieties  ;  and  in  some  cases, 
as  with  domestic  pigeons,  several  otlier  grades  of  dilVerence  are 
requisite.  Nearly  the  same  rules  are  followed  as  in  classifj-ing 
species.  Authors  have  insisted  on  the  necessity  of  arranging 
varieties  on  a  natural  instead  of  an  artificial  system  ;  we  are 
cautioned,  for  instance,  not  to  class  two  varieties  of  the  pine- 
apple together,  merely  because  their  fruit,  though  the  most 
important  part,  happens  to  be  nearly  identical;  no  one  puts 
llie  Swedish  and  conunon  turnijjs  together,  though  the  escu- 
h'nt  and  thickened  stems  are  so  similar.  Whatever  part  is 
found  to  be  most  constant,  is  used  in  classing  varieties  :  thus 
the  great  agriculturist  Marsiiall  says  the  liorns  are  very  useful 
loE  this  purpose  with  cattle,  because  they  are  less  variable  than 
tlie  shape  or  color  of  the  body,  etc. ;  whereas  with  sheep  the 
horns  are  nuicli  less  serviceable,  because  less  constant.  In 
classing  varieties,  I  apprehend  that  if  we  had  a  real  pedigree, 
a  genealogical  classification  would  be  universally  preferred ; 
and  it  has  been  attempted  in  some  cases.  For  we  might  feel 
sure,  wlicther  there  had  been  more  or  less  modification,  the 
])rinciple  of  inheritance  would  keep  the  forms  together  which 
were  alHed  in  the  greatest  number  of  points.  In  tundjler 
])igeons,  tliougli  some  of  the  sul>varieties  difler  in  the  impor- 
tant character  of  having  a  longer  beak,  yet  all  are  kept  togeth- 
er, from  having  the  common  habit  of  tumbling;  but  the  shoit- 
faccd  breed  has  nearly  or  quite  lost  this  haljit;  nevertheless, 
without  any  thought  on  the  sul)ject,  these  tumblers  arc  kept 
in  the  same  group,  because  allied  in  blood  and  alike  in  some 
other  respects. 

With  species  in  a  state  of  nature,  every  naturalist  has  in 
fact  brought  descent  into  his  classification  ;  for  lie  includes  in 
his  lowest  grade,  that  of  the  species,  the  two  sexes  ;  and  how 
enormously  these  sometimes  dilh^r  in  the  most  important  char- 
acters, is  known  to  every  naturalist :  scarcely  a  single  fact  can 
be  predicated  in  common  of  the  adult  males  and  hermajihro- 
•  lites  of  certain  cirripedes,  and  yet  no  one  dreams  of  sejiarating 
ihem.  As  soon  as  the  three  Orchidean  forms,  Monachanthus, 
-Myanthus,  and  Catasetum,  which  had  jireviously  been  ranked 
as  three  distinct  genera,  were  known  to  bo  sometimes  pro- 
duced on  the  same  plant,  they  were  inunediately  considered  as 
varieties;  and  now  1  have  been  able  to  show  that  they  are  the 


382  CLASSIFICATION.  Chap.  XIII. 

male,  female,  and  hermaphrodite  forms  of  the  same  species. 
The  naturalist  ineludes  as  one  species  the  various  larval  stages 
of  the  same  individual,  however  much  they  may  differ  from 
each  other  and  from  the  adult,  as  Avell  as  the  so-called  alter- 
nate generations  of  Stcenslrup,  which  can  only  in  a  technical 
sense  be  considered  as  the  same  individual.  He  includes 
monsters  and  varieties,  not  from  their  partial  resemblance  to 
the  parent-form,  but  because  they  are  descended  from  it. 

As  descent  has  universally  been  used  in  classing  together 
the  individuals  of  the  same  species,  though  the  males  and  fe- 
males and  larvfc  are  sometimes  extremely  different ;  and  as  it 
has  been  nscd  in  classing  varieties  which  have  undergone  a 
certain,  and  sometimes  a  considerable  amount  of  moditication, 
may  not  this  same  element  of  descent  have  been  unconsciously 
used  in  grouping  species  under  genera,  and  genera  imder 
higher  groujis,  all  under  the  so-called  natural  system?  I  be- 
lieve it  has  been  unconsciously  used;  and  thus  only  can  I  im- 
derstand  the  several  rules  and  guides  which  have  been  fol- 
lowed by  our  best  systematists.  We  have  no  written  pedi- 
grees ;  Ave  have  to  make  out  community  of  descent  by  resem- 
blances of  any  kind.  Therefore  Ave  choose  those  characters 
Avhich,  as  far  as  Ave  can  jucige,  are  the  least  likely  to  Ikia'C  been 
modified  in  relation  to  the  conditions  of  life  to  Avhich  each  spe- 
cies has  been  recently  exposed.  Rudimentary  structures  on 
this  vicAV  are  as  good  as,  or  CA'en  sometimes  better  than,  other 
]")arts  of  the  organization.  We  care  not  hoAV  trilling  a  charac- 
tcn-  may  be — let  it  be  the  mere  inflection  of  the  angle  of  the 
jaAv,  the  manner  in  Avhich  an  insect's  Aving  is  folded,  Avhet'licr 
the  skin  be  covered  b}'  hair  or  feathers— if  it  prevail  thn^ugh- 
out  many  and  different  species,  especially  those  haA'ing  very 
different  habits  of  life,  it  assumes  high  A'alue ;  for  Ave  can  ac- 
coimt  for  its  presence  in  so  many  forms  Avith  such  different 
habits,  only  by  inheritance  from  a  common  ]iareut.  A\^e  may 
err  in  this  resjiect  in  regard  to  single  points  of  structure,  but 
Avhen  scA'eral  characters,  let  them  be  eA'cr  so  trifling,  concur 
throughout  a  large  group  of  beings  haA'ing  different  habits,  aa'C 
may  feel  almost  sure,  on  tlieory  of  descent,  that  these  charac- 
ters have  been  inlierited  from  a  common  ancestor.  And  aa-g 
knoAV  that  such  correlated  or  aggregated  charactei's  haA'e  es 
jiecial  value  in  classification. 

We  can  understand  Avhy  a  sjiecies  or  a  group  of  sjiecies 
may  depart,  in  several  of  its  most  important  characteristics, 
from  its  allies,  and  yet  be  safely  classed  Avith  them.     This  may 


Chap.  XIII.  ANALOGICAL  RESEMBLANCES,  3S3 

be  safely  doiip,  aiul  is  often  done,  as  long  as  a  sufficient  num- 
ber of  characters,  let  them  be  ever  so  unimportant,  betrays  the 
hidden  bond  of  community  of  descent.  Let  two  forms  have 
not  a  single  character  in  conunon,  yet  if  these  extreme  forms 
are  connected  together  by  a  chain  of  intermediate  groups,  we 
may  at  once  infer  their  community  of  descent,  and  we  put 
them  all  into  the  same  class.  As  we  find  organs  of  high 
physiologiortl  importance — those  which  serv'C  to  preserve  life 
under  the  most  diverse  conditions  of  existence — are  generally 
the  most  constant,  we  attach  especial  value  to  them ;  but  if 
these  same  organs,  in  another  group  or  section  of  a  group,  are 
found  to  differ  much,  we  at  once  value  them  less  in  our  classi- 
fication. We  sliall  presently  see  why  embryological  charac- 
ters are  of  such  high  classiticatpry  importance.  Geographical 
distribution  may  sometimes  be  brought  usefully  into  play  in 
classing  large  genera,  because  all  the  species  of  the  same 
genus,  inlial)iting  any  distinct  and  isolated  region,  are  in  all 
probability  descended  from  the  same  ]>arents. 

jinalof/lcal  Resemhlanccs. — We  can  understand,  on  the 
above  views,  the  very  important  distinction  between  real  af- 
finities and  analogical  or  adaptive  resemblances.  Lamarck 
first  called  attention  to  this  distinction,  and  he  has  been  ably 
followed  by  Macleay  and  others.  The  resemblance  in  the 
shape  of  the  body  and  in  the  fin-like  anterior  limbs,  between 
the  dugong,  which  is  a  pachydermatous  animal,  and  the 
whale,  and  between  both  these  mammals  and  fishes,  is  analo- 
gical. Among  insects  there  are  innumerable  instances:  tlujs 
Linnicus,  misled  by  external  appearances,  actually  classed  an 
ho;noi)terous  insect  as  a  moth.  We  see  something  of  the  same 
kind  even  in  our  domestic  varieties,  as  in  the  thickened  stems 
of  the  common  and  Swedish  turnips.  The  resemblance  of  the 
greyhound  and  race-horse  is  hardly  more  fanciful  than  the 
analogies  whicli  have  been  drawn  by  some  authors  between 
widely-distinct  animals.  On  my  view  of  characters  being  of 
real  importance  for  classification,  only  in  so  far  as  they  reveal 
descent,  we  can  clearlv  understand  why  analogical  or  adaj^tive 
characters,  although  of  the  utmost  importance  to  the  welfare 
of  tlie  being,  are  almost  valueless  to  the  systematists.  For 
aniiMiils  belonging  to  two  most  distinc-t  lines  of  descent  may 
readily  have  become  adapted  to  similar  conditions,  and  thus 
have  assumed  a  close  external  resemblance ;  but  such  resem- 
blances will  not  reveal — will  rather  tend  to  conceal  their 
blood-rclalionsliip.     We  can  thus  also  understand  the  appar- 


384  ANALOGICAL  KESEMBLANCES.  Chap.  XIIL 

cut  paradox,  that  the  very  same  characters  are  analogical 
when  one  class  or  one  order  is  compared  -with  another,  but 
give  true  aflniities  Avhen  the  members  of  the  same  class  or  or- 
der are  compared  together:  thus,  the  shape  of  the  body  and 
iin-likc  Hmbs  are  only  analogical  "when  whales  are  compared 
AviLli  fishes,  being  adaptations  in  both  classes  for  swimming 
through  the  water;  but  the  shape  of  the  body  and  fin-like 
limbs  serve  as  characters  exhibiting  true  aflinity  between  the 
several  members  of  the  whale  family ;  for  these  cetaceans 
agree  in  so  many  characters,  great  and  small,  that  we  cannot 
doubt  that  they  have  Hiherited  their  general  shape  of  body  and 
structure  of  limbs  from  a  common  ancestor.  So  it  is  with 
fishes. 

The  most  remarkable  case  of  analogical  resemblance  ever 
recorded,  though  not  dependent  on  adaptation  to  similar  con- 
ditions of  life,  is  that  given  by  Mr.  Bates  with  respect  to  cer- 
tain butterflies  in  the  Amazonian  region  closely  mimicking 
other  kinds.  This  excellent  observer  shows  that  in  a  district 
where,  for  instance,  an  Ithomia  abounds  in  gaudy  swarms, 
another  butterfly,  namely,  a  Leptalis,  is  often  found  mingled 
in  the  same  flock,  and  so  closely  resembles  the  Ithomia  in 
every  shade  and  stripe  of  color,  and  even  in  the  shape  of  its 
wings,  that  jNIr.  Bates,  with  his  eyes  sharpened  by  collecting 
during  eleven  years,  was,  though  always  on  his  guard,  con- 
tinually deceived.  When  the  mockers  and  the  mocked  are  caught 
and  comjiared,  they  are  found  to  be  totally  different  in  essen- 
tial structure,  and  to  belong,  not  only  to  distinct  genera,  but 
often  to  distinct  families.  Had  this  mimicry  occurred  in  only 
one  or  two  instances,  it  might  have  been  passed  over  as  a 
strange  coincidence.  But,  if  we  proceed  from  a  district  where 
one  Leptalis  imitates  an  Ithomia,  another  mocking  and  mocked 
species  belonging  to  the  same  genera,  equally  close  in  their  re- 
semblance, will  be  found.  Altogether  no  less  than  ten  genera 
are  enumerated,  which  include  species  that  iinitate  other  but- 
terflies. The  mockers  and  mocked  alwaj's  inhabit  the  same 
region ;  we  never  find  an  imitator  living  remote  from  the 
form  which  it  imitates.  The  mockers  are  almost  invariably 
rare  insects ;  the  mocked  in  almost  every  case  aboimd  in 
swanns.  In  the  same  district  in  which  a  species  of  Lcjitalis 
closely  imitates  an  Ithomia,  there  are  sometimes  other  Lejn- 
doptera  mimicking  the  same  Ithomia ;  so  that  in  the  same 
place,  species  of  three  genera  of  butterflies  and  even  a  moth 
are  found  nil  closely  resembling  a  butterfly  belonging  to  a  fourth 


Chap.  XIII.  ANALOGICAL  EESEMBLANCES.  385 

p^emis.  It  deserves  especial  notice  that  many  of  the  mimick- 
inn^  forms  of  the  Lcptalis,  as  ■well  as  of  the  mimicked  forms, 
can  be  shown  hy  a  g^raduated  series  to  be  merely  varieties  of 
the  same  species ;  while  others  are  undoubtedly  distinct  spe- 
cies. But  why,  it  may  be  asked,  are  certain  Jbrms  treated  as 
tlie  mimicked  and  othei's  as  tlic  mimickers  ?  Mr.  Bates  satis- 
factorily answers  this  question,  by  showing);'  that  the  form 
Avliicli  is  imitated  keeps  the  usual  dress  of  the  f^roup  to  which 
it  lielongs,  while  the  counterfeiters  have  changed  their  dress 
and  do  not  resemble  their  nearest  allies. 

^\'e  are  next  led  to  inquire  what  reason  can  possibly  be  as- 
signed for  certain  butterflies  and  moths  so  often  assuming  the 
dress  of  another  and  quite  distinct  form  ;  why,  to  the  perplexity 
of  naturalists,  has  Nature  condescended  to  the  tricks  of  the 
stage?  ]Mr.  Bates  has,  no  doubt,  hit  on  the  true  explanation. 
The  mocked  forms,  wliich  always  aboimd  in  numbers,  nuist 
habitually  escape  destruction  to  a  large  extent,  otherwise  they 
could  not  exist  in  such  swarms  ;  and  Mr.  Bates  never  saw 
them  preyed  on  l)y  birds  and  certain  large  insects  which  at- 
tack other  butterllies.  He  has  good  reason  to  believe  that 
this  innnunity  is  owing  to  a  peculiar  and  offensive  odor  which 
they  emit.  The  mocking  forms,  on  the  other  hand,  that  in- 
habit the  same  district,  are  comparatively  rare,  and  belong  to 
lare  groups ;  hence  they  must  suffer  habitually  from  some 
danger,  A^r  otherwise,  from  the  number  of  eggs  laid  bv  all  but- 
terflies, they  would  in  three  or  four  generations  swarm  over  the 
wliole  country.  Now  if  a  member  of  one  of  these  persecuted 
and  rare  groups  were  to  assume  a  dress  so  like  that  of  a  well- 
])rotected  species  that  it  continually  deceived  the  practised 
eyes  of  an  entom(ilogist,  it  would  often  deceive  predacious  birds 
and  insects,  and  thus  escape  much  destruction.  Mr.  Bates 
may  almost  be  said  to  have  actually  witnessed  the  process 
by  which  the  mimickers  have  come  so  closely  to  resemble  the 
mimicked  ;  for  he  found  that  some  of  the  forms  of  Lcptalis 
which  mimic  so  many  other  butterflies,  varied  in  an  extreme 
degree.  In  one  district  several  varieties  occurred,  and  of  these 
one  alone  resembled,  to  a  certain  extent,  the  conunon  Ithomia 
of  the  same  district.  In  another  district  there  were  two  or 
three  varieties,  one  of  which  was  much  commoner  than  the 
others,  and  this  closely  mocked  another  form  of  Ithomia. 
From  facts^of  this  nature,  Mr.  Bates  concludes  that  the  I^op- 
talis  first  varies  ;  and  when  a  variety  hajipens  to  resemble  in 
some  degree  any  common  butterfly  inhabiting  the  same  district, 
17 


386  AFFINITIES  CONNECTING  Cuap.  XIII. 

tliis  variety,  from  its  rcseinl)lancc  to  a  flourishing  aiul  little-per- 
secuted kind,  has  a  better  chance  of  escaping'  destruction  from 
predacious  birds  and  insects,  and  is  consequently  oftener  pre- 
served ;  "  the  less  ];)erfect  degrees  of  resemblance  being  gener- 
ation after  generation  eliminated,  and  only  the  others  left  to 
]')ropagate  their  kind."  So  that  here  we  have  an  excellent  il- 
lustration of  natural  selection. 

Mr,  Wallace  has  recently  described  several  equally  striking 
cases  of  mimicry  in  the  Lepidoptera  of  the  Malay  Archipelago, 
and  other  instances  could  be  given  with  other  orders  of  insects. 
Mr.  Wallace  has  also  described  one  case  of  mimicry  among 
birds,  but  we  have  no  such  cases  Avith  the  larger  quadrupeds. 
Tlie  much  greater  fi-equency  of  mimicry  with  insects  than  with 
other  animals,  is  probably  the  consequence  of  their  small  size ; 
insects  cannot  defend  themselves,  excepting  indeed  the  kinds 
that  sting,  and  I  have  never  heard  of  an  instance  of  these 
mocking  other  insects,  though  they  are  mocked ;  insects  can- 
not escape  by  flight  from  the  larger  animals ;  hence  they  are 
reduced,  like  most  weak  creatures,  to  trickery  and  dissimula- 
tion. 

But  to  return  to  more  ordinary  cases  of  analogical  resem- 
l:)lance  :  as  members  of  distinct  classes  have  often  been  adapted 
by  successive  slight  modifications  to  live  under  nearly  similar 
circumstances — to  inhabit,  for  instance,  the  three  elements  of 
land,  air,  and  water — we  can  perhaps  understand  how  it  is  that 
a  numerical  parallelism  has  sometimes  been  observed  between 
the  sub-groups  in  distinct  classes.  A  naturalist,  struck  by  a 
])arallelism  of  this  nature  in  any  one  class,  by  arbitrarily  rais- 
ing or  sinking  the  value  of  the  groups  in  other  classes  (and  all 
our  experience  shows  that  their  valuation  is  as  j'et  arbitrary) 
could  easily  extend  the  parallelism  over  a  wide  range ;  and 
thus  the  septenary,  quinary,  quaternary,  and  ternary  classifica- 
tions have  probably  arisen. 

0)1  tlic  N'ature  of  the  Affinities  connecting  Organic  be- 
ings.— As  the  modified  descendants  of  dominant  species,  be- 
longing to  the  larger  genera,  tend  to  inherit  the  advantages 
which  made  the  groups  to  which  they  belong  large  aud  their 
parents  dominant,  they  are  almost  sure  to  spread  widely,  and 
to  seize  on  more  and  more  places  in  the  economy  of  Nature. 
The  larger  and  more  dominant  groups  within  each  class  thus 
ttMid  to  go  on  increasing  in  size ;  and  they  consecjjiently  sup- 
j>lant  many  smaller  and  feebler  groups.  Thus  wc  can  account 
for  the  fact  that  a]l  organisms,  recent  and  extinct,  are  included 


Chai-.  XIII.  ORGANIC  BEINGS.  337 

under  a  few  p^rcat  orders,  and  under  still  fewer  classes.  As 
sho\vin<j:;  how  few  the  hi<>her  frroups  are  in  number,  and  how 
widely  they  are  spread  throuf^hout  the  world,  the  fact  is  strik- 
in;i-,  that  the  discovery  of  Australia  has  not  added  an  insect 
l)(>l()n<2,"iiij^  to  a  new  class  ;  and  that  in  the  vegetable  kingdom, 
as  I  learn  fi-om  Dr.  Hooker,  it  has  added  only  two  or  three 
families  of  small  size. 

In  the  chapter  on  Geological  Succession  I  attempted  to 
show,  on  the  principle  of  each  group  having  generally  diverged 
nuich  in  character  during  the  long-C(jntinued  process  of  modifi- 
cation, how  it  is  that  the  more  ancient  forms  of  life  often  pre- 
sent characters  in  some  degree  intermediate  between  existing 
groups.  Some  few  of  these  old  and  intermediate  forms  hav- 
ing transmitted  to  the  present  day  descendants  but  little  modi- 
lied,  constitute  our  so-called  osculant  or  aberrant  species.  The 
more  aberrant  any  form  is,  the  greater  must  be  the  number 
of  connecting  forms  Avhicli  have  been  exterminated  and  utterly 
lost.  And  we  hav(!  some  evidence  of  aberrant  groups  having 
suffered  severely  from  extinction,  for  they  are  almost  always 
represented  by  extremely  f(jw  species  ;  and  such  species  as  do 
occur  are  generally  very  distinct  from  each  other,  which  again 
implies  extinction.  The  genera  Ornithorhynchus  and  Lepi- 
(losiren,  for  example,  woulil  not  have  been  less  aberrant  had 
each  been  represented  by  a  dozen  species  instead  of  by  a  single 
one,  or  by  one;  or  two.  We  can,  I  think,  account  for  this  fact 
only  by  looking  at  aberrant  groups  as  forms  which  have  been 
con([uered  by  more  successful  competitors,  with  a  few  mem- 
bers still  preserved  under  unusually  favorable  conditions. 

Mr.  Waterhouse  has  remarked  that,  when  a  member  be- 
longing to  one  group  of  animals  exhibits  an  alTinity  to  a  cpiite 
distinct  group,  this  alVmity  in  most  cases  is  general  and  not 
special :  thus,  according  to  Mr.  Waterhouse,  of  all  Rodents, 
the  bizcacha  is  most  nearly  related  to  Marsupials;  but  in  the 
points  in  which  it  ajiproaches  this  order,  its  relations  are  gen- 
eral, and  not  to  any  one  marsupial  species  more  than  to  an- 
other. As  \]ui  jjoints  of  allinity  are  believed  to  be  real  and 
not  merely  adaptive,  they  nnist  be  due,  in  accordance  with  our 
view,  to  inheritance  from  a  conunon  ])rogenitor.  Therefore  we 
must  su])j)ose  either  that  all  Rodents,  including  the  bizcacha, 
branched  olV  from  some  ancient  Marsupial,  which  will  naturallv 
have  been  more  or  less  intermediate  in  character  with  respect 
to  id!  existing  Marsupials;  or  that  both  Rodents  and  Marsu- 
jjials  branched  olV  iVom   a    cominou  progenitor,  and  that  both 


388  AFFINITIES   CONNECTING  Chap.  XIII. 

g^roups  have  since  undergone  miicli  modification  in  divergent 
directions.  On  citlicr  view  we  must  suppose  that  the  bizcacha 
has  retained,  by  inheritance,  more  of  the  character  of  its  an- 
cient progenitor  than  have  other  Kodents ;  and  therefore  it 
will  not  be  specially  rchited  to  any  one  existing  Marsupial,  but 
indirectly  to  all  or  nearly  all  Marsupials,  from  having  partially 
retained  the  character  of  their  conimon  progenitor,  or  of  some 
earl}"^  member  of  the  group.  On  the  other  hand,  of  all  Mar- 
suj>ials,  as  Mr.  Waterhousc  has  remarked,  the  Phascolomys 
resembles  most  nearly,  not  any  one  species,  but  the  general 
order  of  Rodents.  In  this  case,  however,  it  may  be  strongly 
suspected  that  the  resemblance  is  only  analogical,  owing  to 
the  Phascolomys  having  become  adapted  to  habits  like  those 
of  a  Rodent.  The  elder  De  Candolle  has  made  nearly  similar 
observations  on  the  general  nature  of  the  affinities  of  distinct 
families  of  plants. 

On  the  principle  of  the  multiplication  and  gradual  diver 
gence  in  character  of  the  species  descended  from  a  common 
progenitor,  together  with  their  retention  by  inheritance  of 
some  characters  in  common,  we  can  understand  the  excessively 
complex  and  radiating  affinities  by  which  all  the  members  of 
the  same  family  or  higher  group  are  connected  together.  For 
the  common  progenitor  of  a  whole  family,  now  broken  up  by 
extinction  into  distinct  groups  and  sub-groups,  will  have  trans- 
mitted some  of  its  characters,  modified  in  various  ways  and 
degrees,  to  all  the  species ;  and  they  will  consequently  be 
related  to  each  other  by  circuitous  lines  of  affinity  of. various 
lengths  (as  may  be  seen  in  the  diagram  so  often  referred  to), 
mounting  up  through  many  predecessors.  As  it  is  difficult  to 
show  the  blood-relationship  between  the  numerous  kindred  of 
any  ancient  and  noble  family  even  by  the  aid  of  a  genealogical 
irco,  and  almost  impossible  to  do  so  without  this  aid,  we  can 
understand  the  extraordinary  difficulty  which  naturalists  have 
experienced  in  describing,  without  the  aid  of  a  diagram,  the 
various  affinities  which  tliey  perceive  between  the  many  hving 
and  extinct  members  of  the  same  great  natural  class. 

Extinction,  as  we  have  seen  in  the  fourth  chapter,  has 
played  an  imjiortant  part  in  defining  and  M-idening  the  inter- 
vals between  the  several  groups  in  each  class.  AVe  may  thus 
account  for  the  distinctness  of  whole  classes  from  each  other — 
for  instance,  of  birds  from  all  other  vertebrate  animals — by  the 
belief  that  many  ancient  forms  of  life  have  been  utterly  lost, 
through  which    the  earlv  progenitors  of  l)irds  were   formerly 


CiiAi-.  Xlll.  ORGANIC  BEINGS.  339 

connected  with  the  early  progenitors  of  the  other  and  at  that 
time  less  diirercntiated  vertebrate  classes.  Tlicre  has  been 
less  complete  extinction  of  the  forms  of  life  which  once  con- 
nected fishes  with  batrachians.  There  has  been  still  less  in 
some  other  classes,  as  with  the  Crustacea,  for  here  the  most 
wonderfully  diverse  forms  are  still  linked  together  hy  a  long 
and  only  partially-broken  chain  of  allinities.  Extinction  has 
only  se})arated  the  groups  :  it  has  by  no  means  made  them ; 
for,  if  every  form  which  has  ever  lived  on  this  earth  were  sud- 
denly to  reappear,  tliough  it  would  l)e  cjuite  impossi])le  to  give 
(Iclinitions  by  which  each  group  could  be  distinguished,  still  a 
natural  classification,  or  at  least  a  natural  arrangement,  Avould 
l)c  j)ossible,  AVe  shall  see  this  by  turning  to  the  diagram: 
tlie  letters,  A  to  L,  may  represent  eleven  Silurian  genera,  some 
of  which  have  produced  large  groups  of  modified  descendants, 
Avjtli  every  link  in  each  branch  and  sub-branch  still  alive ;  and 
the  links  not  greater  than  those  between  the  finest  varieties. 
In  this  case  it  would  be  quite  im{)ossible  to  give  definitions  by 
which  the  several  members  of  the  several  groups  could  be  dis- 
tinguished from  their  more  immediate  parents  and  descendants. 
Yet  the  arrangement  in  the  diagram  would  still  hold  good  and 
would  be  natural ;  for,  on  the  principle  of  inheritance,  all  the 
forms  descended,  for  instance,  front  A,  Avould  have  something 
in  common.  In  a  tree  we  can  distinguisli  this  or  that  branch, 
though  at  the  actual  fork  the  two  unite  and  blend  together. 
AV'e  could  not,  as  I  have  said,  define  the  several  groups ;  but 
we  could  pick  out  t\'pes,  or  forms,  representing  most  of  the 
characters  of  each  group,  whether  large  or  small,  and  thus  give 
a  general  idea  of  the  value  of  the  differences  between  them. 
This  is  what  Ave  should  be  driven  to,  if  we  were  over  to  suc- 
c(^ed  in  collecting  all  the  foi-ms  in  any  one  class  which  have 
lived  througliout  all  time  and  sjiace.  Assuredly  we  shall  never 
succeed  in  making  so  perfect  a  colh^ction :  nevertheless,  in  cer- 
tain classes,  we  arc  tending  toward  this  end;  and  Milne  Ed- 
wards has  lately  insisted,  in  an  able  paper,  on  the  high  impor- 
tance of  looking  to  types,  whetlier  or  not  we  can  separate  and 
define  the  groups  to  which  such  types  belong. 

Finally,  we  have  seen  that  natural  selection,  which  results 
from  the  struggle  for  existence,  and  which  almost  inevitably 
leads  to  extinct  ion  and  divergence  of  character  in  the  descend- 
ants from  one  dominant  ]ia rent-species,  explains  that  great  and 
universal  feature  in  tlie  atlinities  of  all  organic  beings,  namely, 
their  suboiilination  in  group  under  group.     We  use  the  clc- 


3'JO  MORPHOLOGY.  Chap.  XIII. 

ment  of  ilrst'cnt  in  chissint!^  the  in(livi<luals  of  both  sexes  and 
of  all  ag"C3  imjcr  one  species,  altliougli  they  niay  hare  but  few 
cliaracters  in  common ;  avc  use  descent  in  chissing  acknowl- 
ed<:;ed  varieties,  liowever  different  they  may  be  from  tlicir  par- 
ent;  and  I  believe  this  element  of  descent  is  the  hidden  bond 
of  connection  -wliich  naturalists  have  sought  under  the  term  of 
the  Natural  System.  On  this  idea  of  the  natural  SA'stem  being, 
in  so  far  as  it  has  been  perfected,  genealogical  in  its  arrange- 
ment, with  tlie  grades  of  difference  exjoressed  by  the  terms 
genera,  families,  orders,  etc.,  we  can  understand  the  rules 
Avhich  we  are  compelled  to  follow  in  our  classification.  We  can 
imderstand  why  we  value  certain  resemblances  far  more  than 
others  ;  why  we  use  rudimentary  and  useless  organs,  or  others 
of  trifling  physiological  importance ;  why,  in  finding  the  rela- 
tions between  one  grouji  and  another,  we  summarily  reject 
analogical  or  adaptive  characters,  and  yet  use  the  same  char- 
acters, within  the  limits  of  the  same  group.  Wc  can  clearly 
see  how  it  is  tliat  all  living  and  extinct  forms  can  be  grouped 
together  within  a  few  great  classes;  and  how  the  several  mem- 
bers of  each  class  are  connected  together  l)y  the  most  complex 
and  radiating  lines  of  affinities.  We  shall  never,  probably, 
disentangle  tlie  inextricable  web  of  the  affinities  between  the 
members  of  any  one  class  ;  but  when  we  have  a  distinct  object 
in  view,  and  do  not  look  to  some  luiknown  plan  of  creation, 
we  mav  hojie  to  make  sure  but  slow  jirogress. 

Prof.  Iliickel,  in  his  "  Generelle  Morphologic  "  and  in  sever- 
al other  works,  has  recently  brought  his  great  knowledge  and 
abilities  to  bear  on  what  he  calls  phylogeny,  or  the  lines  of 
descent  of  all  organic  beings.  In  drawing  up  the  several  se- 
ries he  trusts  chiefly  to  embryological  characters,  but  draws  aid 
from  homologous  and  rudimentary  organs,  as  well  as  from  the 
successive  periods  at  which  the  various  forms  of  life  first  ap- 
peared in  our  geological  formations.  He  has  thus  boldly  made 
a  great  beginning,  and  shows  us  how  classification  will  in  the 
future  l)e  treated. 

Morphology, 

AVe  have  seen  that  the  members  of  the  same  class,  indepen- 
dently of  their  habits  of  life,  resemble  each  other  in  the  general 
j)lan  of  their  organization.  This  resemblance  is  often  expressed 
by  the  term  "  unity  of  t>*])e ; "  or  by  saying  that  the  several 
parts  and  organs  in  the  different  species  of  the  class  are  homol- 


CuAP.  XIII.  MORPHOLOGY.  39I 

ogous.  The  wliole  subject  is  included  under  the  general  term 
of  Morphology.  This  is  the  most  interesting  department  of 
natural  history,  and  )nay  be  said  to  be  its  very  soul.  What 
ean  bo  more  curious  than  that  the  hand  of  a  man,  formed  for 
grasping,  that  of  a  mole  for  digging,  the  leg  of  the  horse,  the 
paddle  of  the  porpoise,  and  the  wing  of  the  Ijat,  should  all  be 
constructed  on  the  same  pattern,  and  should  include  similar 
bones,  ia  the  same  relative  positions  ?  Geoflroy  St.-Hilaire 
has  insisted  strongly  on  the  high  importance  of  relative  posi- 
tion or  connection  in  homologous  parts ;  they  naay  diifer  to 
almost  any  extent  in  form  and  size,  and  yet  will  remain  con- 
nected together  in  the  same  invariable  order.  We  never  find, 
lor  instance,  the  bones  of  the  arm  and  forearm,  or  of  the  thigh 
and  leg,  trans^wsed.  Hence  the  same  names  can  be  given  to 
tJie  homologous  lx)ncs  in  widely-dillercnt  animals.  Wc  see 
the  sanje  great  law  in  the  construction  of  the  mouths  of  in- 
sects ;  what  can  be  more  diflerent  than  the  immensely  long 
spiral  pn>])oscis  of  a  sphinx-moth,  the  curious  folded  one  of  a 
hcc  or  bug,  and  the  great  jaws  of  a  beetle  ? — yet  all  these  or- 
gans, serving  for  such  Avidely-diflerent  purjwses,  are  formed  by 
infinitely-numerous  modifications  of  an  upper  lij"),  mandibles, 
and  two  pal  is  of  maxilkc.  The  same  law  governs  the  con- 
struction of  the  mouths  and  limbs  of  crustaceans.  So  it  is 
with  the  flowers  of  plants. 

Nothing  can  be  more  hopeless  than  to  attempt  to  explain 
this  similarity  of  pattern  in  members  of  the  same  class,  by  util- 
ity or  by  the  doctrine  of  final  causes.  The  hoi^elessness  of  the 
attempt  has  been  expressly  admitted  by  Owen  in  his  most 
interesting  work  on  the  "  Nature  of  Limbs."  On  the  ordinary 
\iew  f)f  the  independent  creation  of  each  being,  we  can  only 
say  that  so  it  is — that  it  has  pleased  the  Creator  to  construct 
all  the  animals  and  plants  in  each  p^eat  class  on  a  uniform 
j)lan :  but  this  is  not  a  scientific  explanation. 

The  exjilanatitjn  is  manifest  according  to  the  theory  of  the 
si'lection  of  successive  slight  modifications — each  modification 
Ijeing  profitable  in  some  way  to  the  modified  form,  but  often 
alVecting  by  correlation  other  parts  of  the  organization.  In 
clianges  of  this  nature,  there  Avill  be  little  or  no  tendency  to 
alter  tlie  origiiud  pattern,  or  to  trans[)ose  the  parts.  The 
l)ones  of  a  limb  might  be  shortened  and  ilattencil  to  any  ex- 
tent, becoming  at  the  same  time  enveloj)ed  in  tliick  membrane, 
so  as  to  serve  as  a  fin  ;  or  a  webbed  liand  might  have  all  its 
bones,  or  certain  bones,  lengthened  to  any  extent,  with  the 


392  MORPHOLOGY.  Ciiai-.  XIII, 

ineinl)rane  connectin*^  them  increased,  so  as  to  serve  as  a  wing; 
yet  all  this  modification  would  not  tend  to  alter  the  framework 
of  the  lx)nes  or  tlie  relative  connection  of  the  parts.  If  wo 
suppose  that  an  early  progenitor — the  archetype  as  it  may  be 
called — of  all  mammals,  had  its  limbs  constructed  on  the  ex- 
isting general  pattern,  for  wliatever  puq->ose  they  served,  we 
can  at  once  perci'ive  the  plain  signification  of  the  homologous 
construction  of  the  limbs  throughout  the  class.  So  ^vith  the 
mouths  of  insects,  we  have  only  to  suppose  that  their  common 
}>rogeiiitor  had  an  upper  lip,  mandibles,  and  two  pair  of  max- 
illiT?,  these  i>arts  being  jjerhaps  very  simple  in  form;  and  then 
natural  selection  will  account  for  the  infinite  diversity  in  the 
structure  and  functions  of  the  mouths  of  insects.  Neverthe- 
less, it  is  conceivable  that  the  general  pattern  of  an  organ 
might  become  so  much  obscured  as  to  be  finally  lost,  by  the 
redaction  and  ultimately  by  the  complete  abortion  of  certain 
jKirts,  by  the  fusion  of  other  parts,  and  by  the  doubling  or  mul- 
tii)li('ation  of  others — variations  which  we  know  to  be  within 
the  limits  of  possibility.  In  the  paddles  of  the  gig-antic  ex- 
tinct sea-lizards,  and  in  the  mouths  of  certain  suctorial  crusta- 
ceans, the  general  pattern  seems  thus  to  have  been  partially 
obscured. 

There  is  another  and  equally  curious  branch  of  our  present 
subject ;  namely,  the  comparison,  not  of  the  same  parts  or  or- 
gans in  different  members  of  the  same  class,  Init  of  the  differ- 
ent parts  or  organs  in  the  same  individual.  Most  physiologists 
believe  that  the  bones  of  the  skvill  are  homologous  with — that 
is,  correspond  in  number  and  in  relative  connection  with — the 
elemental  parts  of  a  certain  number  of  vertebnv.  llie  anterior 
and  pt)sterior  limbs  in  all  the  higher  vertebrate  classes  are 
])lainly  homologous.  So  it  is  with  the  wonderfully  complex 
jaws  and  legs  of  crustaceans.  It  is  familiar  to  almost  every 
one,  that  in  a  flower  the  relative  ]x>sition  of  the  sepals,  petals, 
stamens,  and  pistils,  as  well  as  their  intimate  structure,  are  in- 
telligible on  the  view  that  they  consist  of  metamorphosed 
l(\ives,  arranged  in  a  spire.  In  monstrous  plants,  we  often  get 
direct  evidence  of  the  possibility  of  one  organ  being  transformed 
into  another  ;  and  we  can  actually  see,  during  the  early  or  em- 
bryonic stages  of  development  in  flowers,  as  well  as  in  crusta- 
ceans and  many  other  animals,  that  organs,  which  when  mature 
become  extremely  different,  are  at  first  exactly  alike. 

How  inexplicable  are  these  facts  on  the  ordinary  view  of 
creation !     Why  should  the  brain  be  enclosed  in  a  box  com- 


CiiAr.  XIII.  MOKPIIOLOGY.  393 

posed  of  such  nimicrous  and  such  cxtraordinarily-shajicd  pieces 
of  bone  ?  As  Owen  has  remarked,  the  benefit  derived  from 
tlie  yiokling  of  the  separate  pieces  in  the  act  of  j^arturition  of 
nianiiiials,  will  by  no  means  explain  the  same  construction  in 
the  sl-:ulls  of  birds  and  reptiles.  Why  should  similar  bones 
have  been  created  to  form  the  wiufi;'  and  the  leg-  of  a  bat,  used 
as  they  are  for  such  totally  diflcrcnt  purposes?  Why  should 
one  crustacean,  which  has  an  extremely  complex  mouth  formed 
of  many  parts,  conseciuently  always  have  fewer  leg's  ;  or,  con- 
versely, those  with  many  legs  have  sim])ler  mouths?  ^Vhy 
should  the  sepals,  petals,  stamens,  and  pistils,  in  each  flower, 
tlunigh  litted  for  such  widely-different  purposes,  be  all  con- 
structed on  the  same  pattern  ? 

On  the  theory  of  natural  selection,  we  can  answer  these 
({uestions.  In  the  vertebrata,  Ave  see  a  series  of  internal  verte- 
bra?  bearing  certain  processes;  in  the  arliculata,  the  body  di- 
vided into  a  series  of  segments,  bearing'  external  appendag^es ; 
and,  in  flowering'  plants,  spiral  whorls  of  leaves.  An  indefinite 
repetition  of  the  same  part  or  organ  is  the  common  character- 
istic, as  Owen  has  observed,  of  all  low  or  little-modified  forms; 
therefore  the  unknown  progenitor  of  the  vertebrata  no  doubt 
possessed  man}' vertebrae ;  the  unknown  progenitor  of  the  ar- 
liculata, many  segments;  and  the  unknown  progenitor  of 
(lowering  ])lants,  many  leaves  arranged  in  one  or  more  spires. 
AV(5  have  formerly  seen  that  parts  many  times  repeated  are 
eminently  liable  to  vary  in  number  and  structure.  Conse- 
(juenlly,  such  ])arts  being  already  present,  and  being  highly 
variable,  would  atford  the  materials  for  adaptation  to  the  most 
different  purposes;  and  they  would  generally  retain  through 
the  force  of  inheritance  plain  traces  of  their  original  or  funda- 
mental resemblance. 

In  the  great  class  of  moUusks,  though  it  can  easily  be 
shown  that  the  parts  in  distinct  species  are  homologous,  but 
few  serial  homologies  can  be  indicated ;  that  is,  we  are  seldom 
enabled  to  say  that  one  part  is  homologous  with  another  jiart 
in  the  same  individual.  And  we  can  imdersfand  this  fact ;  for 
ill  mollusks,  even  in  the  lowest  members  of  the  class,  we  do 
not  find  nearly  so  much  indefinite  repetition  of  any  one  part  as 
we  find  in  the  other  great  classes  of  the  animal  and  vegetable 
]>:ingdoms. 

Naturalists  frequently  speak  of  the  skull  as  fonnc.d  of  meta- 
morphosed verlebni' ;  the  jaws  of  crabs  as  metamorphosed  legs; 
the  stamens  and  pistils  in  flowers  as  metamorphosed  leaves ;  but 


394  DEVELOPMENT  Chap.  XIII. 

itwouldinmosl  cases  probably  be  more  corrcrf,  as  Prof.  Huxley 
has  remarked,  to  speak  of  both  skull  and  vertebnc,  both  jaws 
and  lef^s,  etc.,  as  having  been  metamoqihosed,  not  one  from 
the  other,  as  they  now  exist,  but  from  some  common  and 
simpler  clement.  Most  naturalists,  however,  use  such  lan- 
guage only  in  a  metaphorical  sense ;  they  are  far  from  mean- 
ing that,  ckiring  a  long  course  of  descent,  primordial  organs 
of  any  kind — vertebra?  in  the  one  case  and  legs  in  the  other 
— have  actually  been  converted  into  skulls  or  jaws.  Yet  so 
strong  is  the  appearance  of  this  having  occurred,  that  nat- 
uralists can  hardly  avoid  employing  language  having  this 
plain  signification.  According  to  the  views  here  maintained, 
such  language  may  be  used  literally ;  and  the  wonderful  fact 
of  the  jaws,  for  instance,  of  a  crab  retaining  numerous  charac- 
ters, Avhich  they  probably  would  have  retained  through  inheri- 
tance, if  they  had  really  been  metamorjihosed  from  ti-uc  though 
extremely  simple  legs,  is  explained. 

Develojinient  and  Emhryology. 

This  is  one  of  the  most  important  subjects  in  the  whole 
round  of  natural  liistor}^  The  metamorphoses  of  insects,  Avitli 
which  every  one  is  familiar,  are  generally  eflectcd  abruptly  by 
a  few  stages ;  but  the  transformations  are  in  reality  numerous 
and  gradual,  though  concealed.  A  certain  ephemerous  insect 
(Chloeon)  during  its  development,  moults,  as  shown  by  Sir  J. 
Lubljock,  about  twenty  times,  and  each  time  undergoes  a  cer- 
tain amount  of  change ;  and  in  this  case  avc  see  the  act  of 
metamorphosis  performed  in  a  primary  and  gradual  manner. 
Many  insects,  and  especially  certain  crustaceans,  show  us  what 
woiulerful  changes  of  structure  can  be  etTected  during  develop- 
ment. Such  changes,  however,  reach  tlieir  climax  in  the  so- 
called  alternate  generations  of  some  of  the  lower  aTiimals.  It 
is,  for  instance,  an  astonishing  fact  that  a  delicate  branching 
coralline,  studded  with  polypi  and  attached  to  a  submarine 
I'ock,  should  jiroduce,  first  by  budding  and  then  by  transverse 
division,  a  host  of  huge  floating  jelly-lishes ;  and  that  these 
should  ])roduce  eggs,  from  which  are  hatched  swimming  ani- 
malcules, which  attach  themselves  to  rocks  and  become  devel- 
oped into  branching  corallines  ;  and  so  on  in  an  endless  cycle. 
The  belief  in  the  essential  identity  of  the  process  of  alternate 
generation  and  of  ordinary  metamorphosis  has  been  greatly 
strengthened  by  Wagner's  discovery  of  the  larva  or  maggot 


CiiAr.  XIII.  AND   EMBRYOLOGY.  395 

of  a  lly,  namely,  the  Cecidomyia,  producing  ascxually  other 
and  similar  larvie. 

It  has  already  been  stated  that  various  parts  and  organs  in  the 
same  individual  are  exactly  like  each  other  during  an  early  em- 
bryonic period,  but  in  the  adult  state  become  widely  different 
and  serve  for  widely-different  puqioses.  So  again  it  has  been 
slated  that  the  embryos  of  the  most  distinct  species  within  the 
same  class  are  generally  closely  similar,  but  become  when  fully 
developed  widely  dissimilar.  A  better  proof  of  this  latter  fact 
cannot  be  given  than  that  by  Von  15aer,  namely,  that  "  the  em- 
bryos of  mammalia,  of  birds,  lizards,  and  snakes,  probably  also 
of  eheloniii,  are  in  their  earliest  states  exceedingly  like  one 
another,  both  as  a  whole  and  in  the  mode  of  development  of 
their  parts  ;  so  niuch  so,  in  fact,  that  we  can  often  distinguish 
the  emlnyos  only  by  their  size.  In  my  possession  are  two 
little  embryos  in  sj)irit,  whose  names  I  have  omitted  to  attach, 
and  at  ]iresent  I  am  quite  unable  to  say  to  what  class  they  be- 
long. They  may  be  lizards  or  small  birds,  or  very  young- 
mammalia,  so  complete  is  the  similarity  in  the  mode  of  forma- 
tion of  the  head  and  trunk  in  these  animals.  The  extremities, 
however,  are  still  absent  in  these  embryos.  But  even  if  they 
had  existed  in  the  earliest  stage  of  their  development  we 
should  learn  nothing,  for  the  feet  of  lizards  and  mammals,  the 
wings  and  feet  of  birds,  no  less  than  the  hands  and  feet  of 
man,  all  arise  from  the  same  fundamental  form."  The  vermi- 
form larva?  of  moths,  flies,  beetles,  etc.,  generally  resemble  each 
other  much  more  closely  than  do  the  mature  insects ;  but  in 
these  cases  the  embryos  arc  active,  and  from  having  been 
adapted  for  special  lines  of  life  sometimes  differ  much  from 
each  other.  A  trace  of  the  law  of  embryonic  resemblance  oc- 
casionally lasts  till  a  rather  late  age  :  thus  birds  of  the  same 
genus,  and  of  closely-allied  genera,  often  resemble  each  other 
in  their  inunature  plumage  ;  as  Ave  see  in  the  spgtted  feathers 
in  the  young  of  the  thrush  group.  In  the  cat  tribe,  most  of 
the  species  arc  striped  or  spotted  in  lines;  and  stripes  or  spots 
can  be  plainly  distinguished  in  the  whelp  of  the  lion  and  the 
puma.  We  occasionally  though  rarely  sec  something  of  this 
kind  in  ])lants;  thus  the  first  leaves  of  the  ulex  or  furze,  and 
tlu!  lirst  leaves  of  the  j)hyllodincous  acacias,  are  pinnate  or  di- 
vided lik<^  the  ordinary  leaves  of  the  leguminosa\ 

The  points  of  structure,  in  which  the  embryos  of  widely- 
different  animals  within  the  same  class  rcsend^le  each  other, 
often  have  no  tlirect  relation  to  their  conditions  of  existence. 


396  DEVELOPMENT  Chap.  XIII. 

We  cannot,  for  instance,  suppose  tliat  in  the  embryos  of  the 
vcrtebrata  the  pccuhar  loop-like  courses  of  the  arteries.near  the 
branchial  slits  are  related  to  similar  conditions — in  the  young 
mammal  wliich  is  nourished  in  the  womb  of  its  mother,  in  the 
c<rg  of  the  bird  which  is  hatched  in  a  nest,  and  in  the  spawn 
of  a  frog  under  water.  We  have  no  more  reason  to  believe 
in  such  a  relation,  than  we  have  to  believe  that  the  similar 
bones  in  the  hand  of  a  man,  wing  of  a  bat,  and  fm  of  a  por- 
j)oise,  are  related  to  similar  conditions  of  life.  No  one  sup- 
poses tliat  the  stripes  on  the  whelp  of  a  lion,  or  the  spots  on 
the  young  blackbird,  are  of  use  to  these  animals. 

Tlie  case,  however,  is  different  when  an  animal  during  any 
part  of  its  embryonic  career  is  active,  and  has  to  provide  for 
itself.  The  period  of  activity  may  come  on  earlier  or  later  in 
life  ;  but  whenever  it  comes  on,  the  adaptation  of  the  larva  to 
its  conditions  of  life  is  just  as  perfect  and  as  beautiful  as  in  the 
adult  animal.  In  how  important  a  manner  this  has  acted,  has 
recently  been  well  shown  by  Sir  J.  Lubbock  in  his  remarks 
on  the  close  similarity  of  the  larvne  of  some  insects  belonging 
to  very  different  orders,  and  on  the  dissimilarit}^  of  the  larva; 
of  other  insects  within  the  same  order,  according  to  their 
habits  of  life.  From  such  adnptations,  especially  when  they 
im]>ly  a  division  of  labor  during  the  different  stages  of  develop- 
ment, as  Avheu  the  same  larva  has  during  one  stage  to  search 
for  fooil,  and  has  during  another  stage  to  search  for  a  place  of 
attachment,  the  similarity  of  the  lan'te  of  allied  animals  is 
sometimes  greatly  obscured  ;  and  cases  could  be  given  of  the 
larv;V3  of  two  species,  or  of  two  groups  of  species,  differing 
more  from  each  other  than  do  the  adults.  In  most  cases,  how- 
ever, the  larv:c,  though  active,  still  obey,  more  or  less  closel}', 
the  law  of  common  embrj^onic  resemblance.  Cirripedes  afford 
a  good  instance  of  this :  even  the  illustrious  Cuvier  did  not 
perceive  thai  a  barnacle  was  a  crustacean  ;  but  a  glance  at 
the  larva  shows  this  to  be  true  in  an  unmistakable  manner. 
So,  again,  the  two  main  divisions  of  cirripedes,  the  peduncu- 
lated and  sessile,  though  differing  M-idely  in  external  appear- 
ance, have  larvoi  in  all  their  stages  barely  distinguishable. 

The  cml>ryo  in  the  course  of  development  gencrall}-  rises 
in  organization  :  I  use  this  expressiDU,  though  I  am  aware  that 
it  is  hardly  possible  to  deiinc  clearly  what  is  meant  by  the 
organization  being  higher  or  lower.  But  no  one  probably  will 
dispute  that  the  butterfly  is  higher  than  the  caterpillar.  In 
some  cases,  however,  the  mature  animal  nmst  be  considered  as 


Chap.  XIII.  AND  EilBEYOLOGY.  397 

lower  in  the  scale  than  the  larva,  as  witli  certain  parasitic 
crustaceans.  To  refer  once  a<?ain  to  cirripcdes  :  the  larvas  in 
the  lirst  stage  have  three  pairs  of  legs,  a  very  simple  single 
eye,  and  a  proboscifonned  mouth,  with  which  they  feed  largely, 
for  they  increase  much  in  size.  In  the  second  stage,  answer- 
ing to  the  chrysalis  stage  of  butterflies,  they  have  six  pairs  of 
beautifully-constructed  natatory  legs,  a  pair  of  magnificent 
comi)Ound  eyes,  and  extremely  complex  antenmxj ;  but  they 
have  a  close  and  imperfect  mouth,  and  cannot  feed :  their  func- 
tion at  this  stage  is,  to  search  by  their  well-developed  organs 
of  sense,  and  to  reach,  by  their  active  powers  of  swimming,  a 
projier  j)lacc  on  which  to  become  attached  and  to  undergo  their 
final  metamorphosis.  When  this  is  completed,  they  are  fixed 
for  life  :  tlicir  l(\gs  arc  now  converted  into  prehensile  organs  ; 
they  again  obtain  a  well-constructed  mouth  ;  but  they  have  no 
antenna',  and  their  two  eyes  are  now  reconverted  into  a  mi- 
nute, single,  and  very  simple  e^e-spot.  In  this  last  and  com- 
plete state,  cirripedes  may  be  considered  as  either  more  highly 
or  more  lowly  organized  than  they  were  in  the  larval  condi- 
tion. But  in  some  genera  the  larva?  become  developed  either 
into  hermaphrochtes  having  the  ordinary  structure,  or  into 
what  I  have  called  comj)lemcntal  males,  and,  in  the  latter,  the 
development  has  assuredly  been  retiograde  ;  for  the  male  is  a 
mere  sack,  which  lives  for  a  short  time,  and  is  destitute  of 
mouth,  stomach,  or  other  organs  of  importance,  excepting 
those  for  reproduction. 

AVe  are  so  much  accustomed  to  see  a  difference  in  structure 
between  the  embryo  and  the  adult,  that  we  are  tempted  to 
look  at  this  diflerence  as  in  some  manner  necessarily  contin- 
gent on  growth.  But  there  is  no  reason  why,  for  instance,  the 
wings  of  a  bat,  or  the  fins  c^f  a  porpoise,  should  not  have  been 
sketched  t)ut  with  all  their  parts  in  projier  proportion,  as  soon 
as  an}'  structure  became  visible.  In  some  whole  groups  of 
animals  and  in  certain  inemliers  of  other  groups  tin's  is  the 
case,  and  the  cmljryo  does  not  at  any  period  difler  widely  from 
the  adult :  thus  Owen  has  remarked  in  regard  to  cuttle-fish, 
"  there  is  no  metamorphosis  ;  the  ceplialopodic  character  is 
manifested  long  before  the  parts  of  the  embryo  are  com- 
pleted." Land-shells  and  fresh-Avater  crustaceans  are  born 
having  their  proper  form,  while  the  mafine  members  of  the 
same  two  great  classes  pass  through  considerable  and  often 
great  changes  during  their  develoj^ment.  Spiders,  again, 
barely  undergo  any  metamoqihosis.     The  larvae  of  most  insects 


398  DEVELOPMENT  Chap.  XIII. 

pass  throuu'li  a  worm-like  sta_o;o,  Avhcthcr  they  arc  active  and 
adapted  to  diversified  habits,  or  are  inactive  from  lieing  placed 
in  the  midst  of  proper  nutriment  or  from  bcinpf  fed  by  their 
parents ;  but  in  some  few  cases,  as  in  that  of  Aphis,  if  we  look 
to  the  admiraljle  drawings  of  the  development  of  this  insect,  by 
Prof.  Huxley,  wc  sec  hardly  any  trace  of  the  vermiform  stage. 

Sometimes  it  is  only  the  earlier  developmental  stages 
which  fail.  Thus  Fritz  Miiller  has  made  the  remarkable  dis- 
covery tliat  certain  shrimp-like  crustaceans  (allied  to  Penoeus) 
first  appear  imder  the  simple  nauplius-form,  and  after  passing 
through  two  or  more  zoea-stages,  and  then  through  the  mysis- 
stage,  finally  acquire  their  mature  structure  :  now  in  the  Avhole 
great  malacostracan  class,  to  which  these  crustaceans  belong, 
no  other  member  is  as  yet  known  to  be  first  developed  under 
the  nau})lius-form,  though  many  appear  as  zoeas;  nevertheless, 
Miiller  assigns  reasons  for  his  belief  that  all  these  crustaceans 
would  luiA-c  appeared  as  nauplii,  if  tliere  had  been  no  suppres- 
sion of  development. 

How,  then,  can  we  explain  these  several  facts  in  embryology 
— namely,  the  very  general,  though  not  universal,  diflerence 
in  structure  between  the  embryo  and  the  adult — the  various 
parts  in  the  same  individual  embryo,  which  ultimately  become 
very  unlike  and  serve  for  diverse  purposes,  being  at  an  early 
period  of  growth  alike — the  general,  but  not  invariable,  resem- 
blance between  the  embryos  or  larvre  of  the  most  distinct 
species  in  the  same  class — the  embryo  retaining,  Avhile  within 
the  egg  or  womb,  structures  which  are  of  no  service  to  it, 
either  at  that  period  or  later  in  life ;  Avhile  embryos  at  a  later 
]icriod,  or  larvie,  which  have  to  provide  for  their  own  wants, 
are  perfectly  adapted  to  the  surrounding  conditions — and  lastly 
the  fact  of  certain  larvas  standing  higher  in  the  scale  of  organi- 
zation than  the  mature  animals  into  which  they  are  developed  ? 
I  believe  tliat  all  these  facts  can  be  explained,  as  follows  : 

It  is  commonly  assumed,  perhaps  from  monstrosities  affect- 
ing the  embryo  at  a  very  early  period,  that  slight  variations  or 
individual  dilferences  necessarily  appear  at  an  equally  early 
l)eriotl.  ^Vc  have  little  evidence  on  this  head,  but  what  we 
liave  certainly  points  the  other  way ;  for  it  is  notorious  that 
l)recders  of  cattle,  horses,  and  various  fancy  animals,  cannot 
positively  tell,  until  "some  time  after  birth,  what  the  merits  or 
form  of  their  young  animals  will  turn  out.  We  see  this  plainly 
in  our  own  children  ;  wc  cannot  tell  whether  a  child  Avill  be 
tall  or  short,  or  what  its  jirecise  features  will  be.     The  ques- 


CuAP.  XIII.  AND  EMBRYOLOGY.  399 

tion  is  not,  at  what  period  of  life  each  vaiiation  may  have  been 
caused,  but  at  wliat  period  the  effects  arc  disphiyed.  The 
cause  may  have  acted,  and  I  beheve  generally  has  acted,  on 
one  or  both  parents  before  reproduction.  It  deserves  notice 
that  it  is  of  no  importance  to  a  very  yoimi^  animal,  as  long  as 
it  remains  in  its  mother's  womb  or  in  the  egg,  or  as  long  as  it 
is  nourished  and  protected  by  its  parent,  wlicther  most  of  its 
characters  are  acquired  a  little  earlier  or  later  in  life.  It 
"would  not  signify,  for  instance,  to  a  bird  Avhich  obtained  its 
food  by  having  a  much-curved  beak,  Avhether  or  not  "while 
young  it  possessed  a  beak  of  this  shape,  as  long  as  it  was  fed 
by  its  parents. 

I  have  stated,  in  tlu^  first  chapter,  that  at  whatever  age  a 
variation  first  appears  in  the  parent,  it  tends  to  reappear  at  a 
corresponding  age  ni  tlie  offsjiring.  Certain  variations  can 
only  appear  at  corresponding  ages:  for  instance,  peculiarities 
in  the  caterpillar,  cocoon,  or  imago  states  of  the  silk-moth  ;  or, 
again,  in  the  full-grown  horns  of  cattle.  But  variations, 
which,  for  all  that  we  can  see  might  have  appeared  either  ear- 
lier or  later  in  life,  likewise  tend  to  appear  at  a  corresponding 
age  in  the  offspring  and  parent.  I  am  far  from  meaning  that 
this  is  invariably  the  case ;  and  I  could  give  several  excep- 
tional cases  of  variations  (taking  the  word  in  the  largest  sense) 
which  have  supervened  at  an  earlier  age  in  the  child  than  in 
the  parent. 

These  two  principles,  namely,  that  slight  variations  gener- 
ally appear  at  a  not  very  early  period  of  life,  and  are  inher- 
ited at  a  corresponding  not  early  period,  explain,  as  I  believe, 
all  the  aljove  specilieil  leading  facts  in  embryology.  But  first 
let  us  look  to  a  few  analogous  cases  in  our  domestic  varieties. 
Some  authors  who  have  written  on  Dogs,  maintain  that  the 
greyhound  and  bull-dog,  though  a})pearing  so  different,  are 
really  closely-allied  varieties,  descended  from  the  same  wild 
stock;  hence  I  was  curious  to  see  how  far  their  puppies  dif- 
fered from  each  other:  I  was  told  by  breeders  that  they  dif- 
fered just  as  much  as  their  parents,  and  this,  judging  by  the 
eye,  seemed  almost  to  l)e  the  case  ;  but  on  actually  measuring 
the  old  dogs  and  their  six-days-old  jnijipies,  I  found  that  the 
]>iipI)i('S  had  not  acquired  nearly  their  full  amount  of  propor- 
tional difference.  So,  again,  I  was  t(jld  that  the  foals  of  cart 
and  race  lujrses — breeds  which  have  been  almost  wholly  formed 
by  selection  imder  domestication — differed  as  mmh  as  the  full- 
grown  animals  ;  but  having  had  careful  measurements  made 


400  DEVELOPMENT  Chap.  XIII. 

of  llic  dciiiis  and  of  threc-days-old  colts  of  racc-horscs  and 
heavy  cart-horses,  I  find  tliat  tliis  is  by  no  means  tlic  case. 

As  we  have  conckisivc  ev-idcnce  that  the  breeds  of  the  Pig- 
con  are  descended  from  a  single  -wild  species,  I  compared  the 
young  within  twelve  hours  after  being  hatched ;  I  carefully 
measured  in  the  wild  jnu-ent-species,  in  pouters,  fantails,  runts, 
barl)s,  dragons,  carriers,  and  tumblers,  the  i)roportlons  (but 
will  not  here  give  the  details)  of  the  beak,  width  of  mouth, 
length  of  nostril  and  of  eyelid,  size  of  feet  and  length  of  leg. 
Now  some  of  these  birds,  Avhen  mature,  differ  in  so  extraor- 
dinary a  degree  in  the  length  and  form  of  beak,  and  in  other 
characters,  that  they  would  certainly  be  ranked  as  distinct 
genera  if  found  in  a  state  of  nature.  But  when  the  nestling 
birds  of  these  several  breeds  were  placed  in  a  row,  though 
most  of  them  could  just  be  distinguished,  yet  the  projiortional 
differences  in  the  above-specified  points  were  incomparably 
less  than  in  the  full-grown  birds.  Some  characteristic  points 
of  difference — for  instance,  that  of  the  width  of  mouth — could 
hardly  be  detected  in  the  young.  But  there  was  one  remark- 
able excejition  to  this  rule,  for  the  young  of  the  short-faced 
tumbler  difiered  in  all  its  proportions  from  the  young  of  the 
wald  rock-pigeon  and  of  the  other  breeds,  almost  exactly  as 
much  as  in  the  adult  state. 

The  above  two  principles  explain  these  facts.  Fanciers 
select  for  breeding  their  dogs,  horses,  pigeons,  etc.,  when 
nearly  grown  \ip :  they  are  indifferent  whether  the  desired 
qualities  arc  acquired  earlier  or  later  in  life,  if  the  full-grown 
animal  possesses  them.  And  the  cases  just  given,  more  espe- 
cially that  of  pigeons,  show  that  the  characteristic  differences 
which  give  value  to  the  breeds,  and  which  have  been  accumu- 
lated by  man's  selection,  have  not  generally  appeared  at  a  very 
early  period  of  life,  and  have  been  inherited  at  a  corresponding 
not  early  period.  But  the  case  of  the  short-faced  tumbler, 
which  when  twelve  hours  old  possessed  its  ]iroper  characters, 
proves  that  this  is  not  the  imiversal  rule  ;  for  here  the  charac- 
teristic dillerences  must  either  have  appeared  at  an  earlier 
period  than  usual,  or,  if  not  so,  the  differences  must  have  been 
inlieritcd,  not  at  a  corresponding,  but  at  an  earlier  age. 

Now  let  us  ajiply  these  two  principles  to  species  in  a  state 
of  nature.  Let  us  take  a  group  of  birds,  desccmded  from  some 
ancient  form  and  modified  through  natinwl  selection  for  differ- 
ent habits.  Then,  from  the  many  slight  successive  variations 
having  supervened  in  the  several  species  at  a  not  early  age, 


Cii.vr.  XIII.  AND  EMBRYOLOGY.  401 

and  having  been  inherited  at  a  corresponding  age,  the  young 
will  be  left  l)iit  little  modifuMl  and  will  resemble  each  other 
much  more  closely  than  do  the  adults — just  as  we  have  seen 
with  the  breetls  of  the  pigeon.  We  may  extend  this  view  to 
widely-distinct  structures  and  to  whole  classes.  The  fore- 
liiiihs,  for  instance,  which  once  served  as  legs  to  a  remote  ])ro- 
genitor,  may  have  become,  through  a  long  course  of  modiJica- 
tioii,  adapted  in  one  descendant  to  act  as  hands,  in  another  as 
paddles,  in  another  as  wings  ;  but  on  the  above  two  principles 
the  fore-limbs  will  not  have  been  much  modified  in  the  embryos 
of  these  several  forms ;  although  in  each  the  embryonic  forc- 
liinb  will  differ  greatly  from  that  in  the  adult.  Whatever  in- 
fluence, moreover,  long-continued  use  or  disuse  may  have  had 
in  modifying  the  limbs  or  other  parts  of  animals,  this  will 
chiefly  or  solely  have  affected  them  when  mature,  and  when 
they  hatl  to  use  their  full  powers  to  gain  their  own  living; 
and  the  elTect  thus  jiroduced  will  be  transmitted  to  the  oil- 
spring  at  a  ccjrrcsponding  mtitvn'e  age.  Thus  the  young  will 
not  be  modified  or  will  be  modiiied  in  a  less  degree. 

In  other  cases  successive  variations  may  have  supervened 
at  a  very  early  period  of  life,  or  the  steps  may  have  been  in- 
herited at  an  earlier  age  than  that  at  which  they  first  occurred. 
In  either  case,  as  we  have  seen  Avith  the  short-faced  tumbh^r, 
the  young  or  embryo  would  closely  resemble  tlie  mature  par- 
ent-form. And  this  is  the  rule  of  development  in  certain  whole 
groups  or  sub-grouj^s,  as  Avith  cuttle-fish,  land-shells,  fresh-wa- 
ter crustaceans,  spiders,  and  some  members  of  the  great  class 
of  insects.  AVith  respect  to  the  fmal  cause  of  the  3'^oung  in 
these  groups  not  passing  through  any  metamorphosis,  we  can 
see  that  this  would  follow  from  the  following  contingencies ; 
namely,  from  the  young  having  to  provide  at  a  very  early  age 
for  Iheir  own  Avants,  and  from  their  following  the  same  habits 
of  life  with  their  parents ;  for,  in  this  case,  it  would  be  indis- 
]iensable  for  their  existence  that  they  should  be  modiiied  in 
the  same  manner  as  their  parents.  Again,  with  respect  to  the 
singular  fact  of  so  many  terrestrial  and  fresh-water  animals  not 
undergoing  any  metamorphosis,  while  marine  members  of  the 
same  groups  pass  through  various  1  ransformal  ions,  Fritz  MuUer 
has  suggested  that  the  process  of  slowlv  modifying  and  adapt- 
mg  an  animal  to  live  on  the  land  or  in  fresh  water,  insttnvd 
of  in  the  sea,  would  be  greatly  simjjliHed  by  its  not  passing 
through  any  larval  stage  ;  for  it  is  not  probable  that  places  well 
adapted  for  both  the  larval  and  mature  stages,  under  such  new 


402  DEVELOPMENT  CiiAr.  XIII. ' 

and  greatly-changed  habits  of  life,  could  be  found  unoccupied 
or  ili-occupit'd  by  other  organisms.  In  this  case  the  gradual 
acquirement  at  an  earlier  and  earlier  age  of  the  adult  structure 
would  be  favored  by  natural  selection,  and  all  traces  of  formei 
metamorphoses  would  finally  be  lost. 

If, on  the  oilier  liand,  it  })rofitetl  the  young  of  an  animal  to 
follow  hal)its  of  life  slightly  dillerent  from  those  of  the  parent- 
form,  and  consequently  to  be  constructed  in  a  slightl^'-dif- 
ferent  manner,  or  if  it  profited  alarva  already  widely  different 
from  its  parent  to  change  still  further,  then,  on  the  principle 
of  inheritance  at  corresponding  ages,  the  young  or  the  larvas 
might  be  rendered  by  natural  selection  more  and  more  differ- 
ent from  their  parents  to  any  conceivable  extent.  Differences 
in  the  larvie  might,  also,  become  correlated  with  successive 
stages  of  development ;  so  that  the  larvee,  in  the  first  stage, 
might  come  to  differ  gTcatly  from  the  larva?  in  the  second 
stage,  as  is  the  case  Avith  many  animals.  The  adult  might 
also  become  fitted  for  sites  or  habits,  in  which  organs  of  loco- 
motion or  of  the  senses,  etc.,  would  be  useless ;  and  in  this 
case  the  metamorphosis  would  be  retrograde. 

From  the  remarks  just  made,  we  can  see  how  by  changes 
of  structure  in  the  young,  in  conformity  Avith  changed  habits 
of  lif(%  together  with  inheritance  at  corresponding  ages,  animals 
in  certain  cases  might  come  to  pass  through  stages  of  develop- 
ment, perfectly  distinct  from  their  primordial,  adult  condition. 
Fritz  Muller,  Avho  has  recently  discussed  this  subject  with  much 
ability,  believes  that  the  progenitor  of  all  insects  resembled  an 
adult  insect,  and  that  the  caterpillar  or  maggot  stages,  as 
Avell  as  the  cocoon  or  pupal  stages,  have  subsequently  been  ac- 
(|uired;  but  from  this  view  many  naturalists,  for  instance,  Sir 
J.  Lubbock,  who  has  likewise  recently  discussed  this  subject, 
would,  it  is  probable,  dissent.  That  certain  unusual  stages  in 
the  metamorphoses  of  insects  have  been  acquired  through  adap- 
tation to  peculiar  habits  of  life,  there  can  hardly  be  a  doubt ; 
thus  the  hrst  larval  form  of  a  certain  beetle,  the  Sitaris,  as  de- 
scribed by  M.  Fabre,  is  an  active,  minute  insect,  furnished  with 
six  legs,  two  long  antenna^,  and  four  eyes.  These  larvro  are 
hatched  in  the  nests  of  bees ;  and  Avhen  the  male-bees  emerge 
fiom  their  burrows  in  the  spring,  which  they  do  before  the 
females,  the  larvte  spring  on  them,  and  afterward  crawl  on  the 
female  while  paired  with  the  males.  As  soon  as  the  females 
lay  their  eggs  on  tlie  surface  of  the  honey  stored  in  their  cells, 
the  larvas  of  the  Sitaris  leap  on  the  eggs  and  devour  them. 


CiiAr.  XIH.  AND  EMBIIYOLOGY.  -40:} 

Afterward  these  lan'flQ  undergo  a  complete  change ;  their  eyes 
disapjiear ;  tlicir  legs  and  autenna3  become  rudimentary-,  and 
tl ley  feed  on  honey ;  so  that  they  now  more  closely  reseniljlc 
the  ordinary  larva?  of  insects ;  ultimately  they  undergo  a  fur- 
ther transformation,  and  hnally  emerge  as  the  perfect  beetle. 
Now,  if  an  insect,  undergoing  transformations  like  those  of  the 
Sitaris,  were  to  become  the  progenitor  of  a  whole  new  class 
of  insects,  their  course  of  development  would  probably  be 
M-idely  dillerent  from  what  it  now  is ;  and  the  hrst  larval  stage 
certainly  would  not  represent  the  former  condition  of  any 
adult  and  ancient  insect. 

On  the  other  hand,  it  is  highly  probable  that  with  many 
animals  the  embryonic  or  larval  stages  show  us,  more  or  less 
coni])letely,  the  state  of  the  progenitor  of  the  whole  group  in 
its  adult  condition.  In  the  great  class  of  the  Crustacea,  forms 
wondeifully  distinct  from  each  other,  namely,  suctorial  para- 
sites, cirripedes,  entomostraca,  and  even  the  malacostraca,  ap- 
pear at  iirst  as  larva;  imder  the  nauplius-form ;  and  as  these 
larva;  feed  and  live  in  the  open  sea,  and  are  not  adapted  for 
any  peruliar  habits  of  life,  and  from  other  reasons  assigned  by 
Fritz  Midler,  it  is  probable  that  an  independent  adult  animal, 
i-estMubling  the  nauplius,  existed  at  some  very  remote  period, 
and  subsef(ncntly  produced,  along  several  diverg(;nt  lines  of 
descent,  the  several  above-named  great  Crustacean  groups. 
So  again  it  is  pr(»l:)able,  fi-om  what  we  know  of  the  emljryos  of 
mannnals,  birds,  fishes,  and  reptiles,  that  these  animals  are  the 
niodilied  descendants  of  some  one  ancient  progenitor,  which 
Avas  furnished  in  its  adult  state  with  branchia',  a  swim-1)ladder, 
four  simple  limbs,  and  a  long  tail,  all  fitted  for  an  aquatic  life. 

As  all  the  organic  beings,  extinct  and  recent,  which  have 
ever  lived,  can  be  arranged  within  a  few  great  classes ;  and  as 
all  within  each  class  have,  according  to  our  theory,  formerly 
licen  connected  together  by  fine  gradations,  the  best,  and,  if 
our  collections  were  nearly  perfect,  the  only  possible  arrange- 
ment, would  be  genealogical;  descent  being  the  hidden  bond 
(if  connection  which  naturalists  have  been  seeking  vmder  the 
term  of  the  Natural  System.  On  tliis  view  we  can  under- 
stand how  it  is  that,  in  the  eyes  of  most  naturalists,  the 
structure  of  the  eml)ryo  is  even  more  important  for  classifica- 
lion  than  that  of  the  adult.  In  two  or  more  groups  of  ani- 
mals, however  much  they  may  dilTer  from  each  other  in  struct- 
ure and  habits,  if  they  pass  tlirough  closely  similar  embryonic 
stagt'S,  we  may  feel  assured  that  they  all  arc  descended  from  one 


iO\  RUDIMENTARY,   ATEOPIIIED,  Chap.  XHI. 

parent-form,  and  are  therefore  closely  related.  Thus,  coumumi- 
iy  in  emlHyonic  structure  reveals  community  of  descent ;  but 
dissimilarity  in  embryonic  development  does  not  prove  discom- 
munity  of  ilescent,  for  in  one  of  two  groups  the  developmental 
stages  may  have  been  suppressed,  or  may  have  been  so  greatly 
modified  through  adaptation  to  new  habits  of  life,  as  to  bo 
no  longer  recognizaljle.  Even  in  groups,  in  which  the  adults 
have  been  moditied  to  an  extreme  degree,  community  of 
origin  is  often  revealed  by  the  structure  of  the  larva? ;  we  have 
seen,  for  instance,  that  cirripedes,  though  externally  so  like 
shell-fish,  are  at  once  known  by  their  larvae  to  belong  to  the 
gTeat  class  of  crustaceans.  As  the  structure  of  the  cmbrj-o 
generally  shows  us  more  or  less  plainly  the  structure  of  its  less 
modified  and  ancient  progenitor,  Ave  can  see  why  ancient  and 
extinct  forms  so  often  resemble  the  embryos  of  existing  spe- 
cies in  the  same  class.  Agassiz  believes  this  to  be  a  univer- 
sal law  of  Nature ;  and  I  hope  to  see  it  hereafter  shown  in 
most  cases  true.  It  can,  however,  be  proved  true  only  in 
those  cases  in  which  the  ancient  state  has  not  been  wholly  ob- 
literated either  by  successive  variations  being  supervened  at  a 
very  early  period  of  growth,  or  by  such  variations  having  been 
inherited  at  an  earlier  period  than  that  at  which  they  first  ap- 
peared. It  should  also  be  borne  in  mind,  that  the  law  may  be 
true,  but  yet,  o\ving  to  the  geological  record  not  extending  far 
enough  back  in  time,  may  remain  for  a  long  period,  or  for  ever, 
incapable  of  demonstration.  The  laAV  will  not  hold  good  in  those 
cases  in  which  an  ancient  form  became  adapted  in  its  larval 
state  to  some  special  line  of  life,  and  transmitted  the  same  larval 
state  to  a  whole  group  of  descendants ;  for  these  in  their  lar^'al 
condition  will  not  resemble  any  ancient  form  in  its  adult  state. 
Thus,  as  it  seems  to  me,  the  leading  facts  in  embryology, 
M'hich  are  second  to  none  in  importance,  are  explained  on  the 
principle  of  modifications  in  the  many  descendants  from  some 
one  ancient  progenitor,  not  having  appeared  at  an  early  period 
of  life,  and  having  been  inherited  at  a  corresponding  period. 
Embryology  rises  greatly  in  interest,  when  we  look  at  the  em- 
bryo as  a  picture,  more  or  less  obscured,  of  the  progenitor,  either 
in  its  adult  or  larval  state,  of  all  the  members  of  the  same 
great  class. 

liudimentart/,  Atrophied,  and  Aborted  Organs. 

Organs  or  jiarts  in  this  strange  condition,  bearing  the  plain 
stamp  of  inutihtv,  arc    extremely  common,  or  even   general 


Chap.  XIII.  AND   ABOIITED   ORGANS.  405 

lliroiighout  Nature.  It  'would  be  difficult  to  name  one  of  the 
his/her  animals  in  which  some  part  is  not  in  a  rudimentary 
condition.  In  the  mammalia,  for  instance,  the  males  always 
possess  rudimentary  mamma?;  in  snakes  one  lobe  of  the  lunj^s 
is  rndimentary ;  in  birds  the  "bastard-wing"  may  safely  be 
considered  as  a  rudimentary  digit,  and  in  not  a  few  species  the 
wings  cannot  be  used  for  ilight  or  are  reduced  to  a  rudiment. 
AVhat  can  be  more  curious  than  the  presence  of  teeth  in 
fetal  whales,  which  when  grown  up  have  not  a  tooth  in  their 
heads;  or  the  teeth,  which  never  cut  through  the  gums,  in  the 
upper  jaws  of  unliorn  calves  ? 

Hudimentary  organs  declare  their  origin  and  plain  meaning 
in  various  wa3's.  There  are  beetles  belonging  to  closely-allied 
species,  or  even  to  the  same  identical  species,  which  have 
either  full-sized  and  perfect  wings,  or  mere  minute  rudiments 
of  membrane,  not  rarely  lying  under  wing-covers  firmly 
soldered  together ;  and  in  this  case  it  is  impossible  to  doubt 
that  the  rudiments  represent  wings.  Rudimentary  organs 
sometimes  retain  tlieir  potentiality ;  this  occasionally  occurs 
with  the  mamma?  of  n)ale  mammals,  for  they  have  been  known 
to  become  well  developed,  and  to  secrete  milk.  So  again  in 
the  udders  in  the  genus  Bos,  there  are  normally  four  developed 
and  two  rudimentary  teats ;  but  the  latter  in  our  domestic 
cows  sometimes  become  well  developed  and  yield  milk.  In 
regard  to  plants  the  petals  are  sometimes  rudimental,  and 
sometimes  well-develojied  in  individuals  of  the  same  species. 
In  certain  dicccious  ])lants  Kolreuter  found  that  by  crossing  a 
species,  in  which  the  male  flowers  included  a  rudiment  of  a 
jiistil,  with  an  hermaphrodite  species,  having  of  course  a  Avell- 
devel()j)ed  ])istil,  the  rudiment  in  the  hybrid  ofl'spriiig  Avas 
nuich  increased  in  size ;  and  this  clearly  shows  that  the  rudi- 
mentary and  perfect  pistils  are  essentially  alike  in  nature.  An 
animal  may  ])ossess  various  parts  in  a  perfect  state,  and  yet 
they  may  in  one  sense  be  rudimentary,  for  they  are  useless: 
thus  tlie  tadpole  of  the  connnon  Salamander  or  newt,  as  Mr. 
G.  II.  Lewes  remarks,  "lias  gills,  and  passes  its  existence  in 
the  water;  but  the  Salamandra  atra,  which  lives  high  up 
among  the  mountains,  brings  forth  its  young  full-formed.  This 
.•'.nimal  never  lives  in  the  water.  Yet  if  we  open  a  gravid  le- 
male,  we  find  tadpoles  inside  her  with  exquisitt^ly-feathered 
gills  ;  and  when  jilaced  in  water  they  swim  about  like  the  t^id- 
])oles  of  the  water-newt.  Obviously,  this  aquatic  organization 
has  no  reference  to  the  future  life  of  the  animal,  nor  has  it  any 


40G  KUDIMENTAHV,   ATROPHIED,  Chat.  XIII. 

adaptation  to  its  cniljrvonic  condition ;  it  has  solely  reference 
to  ancestral  adaptations,  it  repeats  a  phase  in  the  development 
of  its  profi^enitors." 

An  ornj-an,  serving;  for  two  purposes,  may  become  rudimen- 
tary or  utterly  aborted  for  one,  even  the  more  important  pur- 
pose, and  remain  perfectly  eflicient  for  the  other.  Thus  in 
plants,  the  oflice  of  the  pistil  is  to  allow  the  pollen-tubes  to 
reach  the  ovules  -within  the  ovarium.  The  pistil  consists  of  a 
stigma  supported  on  a  style ;  but  in  some  Composita?,  the 
male  florets,  which  of  course  cannot  bo  fecundated,  have  a  ru- 
dimentary pistil,  for  it  is  not  crowned  with  a  stigma ;  but  the 
stylo  remains  Avell  developed,  and  is  clothed  with  hairs,  in  the 
usual  manner,  for  brushing  the  pollen  out  of  the  suiTOunding 
and  conjoined  anthers.  Again,  an  organ  may  become  rudi- 
mentary for  its  proper  purpose,  and  be  used  for  a  distinct  ob- 
ject :  in  certain  fish  the  swim-bladder  seems  to  be  nearly  rudi- 
mentary for  its  proper  function  of  giving  buoj-ancy,  but  has 
become  converted  into  a  nascent  breathing-organ,  or  lung. 
Other  similar  instances  could  be  given. 

Organs,  however  little  developed,  if  of  use,  should  not 
be  considered  as  rudiincntarv :  they  may  be  called  nascent, 
and  may  hereafter  be  developed  by  natural  selection  to  any 
further  extent.  Kudimentary  oigans,  on  the  other  hand,  are 
essentially  useless,  as  teeth  which  never  cut  through  the  gums. 
As  they  would  be  of  even  less  use,  Avhen  in  a  still  less  devel- 
oped condition,  they  cannot  have  been  formed  through  varia- 
tion and  natm-al  selection,  which  latter  acts  solely  by  the  pres- 
ervation of  useful  modilications.  They  relate  to  a  former 
state  of  things,  and  have  been  partially  retained  by  the  power 
of  inheritance.  It  is  difficult  to  know  what  organs  are  nas- 
cent ;  looking  to  the  future,  we  cannot  of  course  tell  how 
any  part  will  be  developed,  and  whether  it  is  now  in  a  nascent 
condition  ;  looking  to  the  past,  creatures  with  an  organ  in  this 
condition  will  generally  have  been  supplanted  by  their  suc- 
cessors with  the  same  organ  in  a  more  perfect  state,  and  con- 
sequently will  have  become  long  ago  extinct.  The  wing  of 
the  penguin  is  of  high  service,  acting  as  a  fin ;  it  may,  there- 
fore, represent  the  nascent  state  of  the  Aving ;  not  that  I  be- 
li(>ve  this  to  be  the  case ;  it  is  more  probably  a  reduced  organ, 
modilied  for  a  new  function:  the  wing  of  the  Apteryx,  on  the 
otiier  hand,  is  c[uite  useless,  and  is  ti-uly  rudimentary.  Tlic 
simple  lilamentary  limbs  of  the  Lepidosiren  ajiparently  are  in 
a  nascent   state;  for,   as  Owen   lias    remarked,  th(>v   are   the 


Chap.  XIII.  AND  ABORTED   ORGANS.  407 

"  Ijpo^liuiinjif.s  of  oro^ans  which  attain  full  functional  develop- 
ni(Mit  in  hiij^hcr  verteliratcs."  The  mammary  j^lands  of  the 
Oniithorhyncluis  may  be  considered,  in  comparison  Avith  the 
udders  of  a  cow,  as  in  a  nascent  condition.  The  oviji^erous 
frena  of  certain  cirripodes,  which  are  only  slightly  developed, 
and  which  have  ceased  to  give  attachment  to  the  ova,  are  nas- 
cent branchiir. 

Rudimentary  organs  are  very  liable  to  vary  in  development 
and  in  other  respects  in  the  individuals  of  the  same  species. 
Moreover,  in  closely-allied  species,  the  degree  to  which  the 
same  organ  has  been  reduced  occasionally  differs  much.  Tiiis 
latter  fact  is  well  exemplilied  in  the  state  of  the  wings  in  fe- 
male moths  in  certain  group.s.  Rudimentary  organs  may  be 
utterly  aborted ;  and  this  implies  that,  in  certain  animals  or 
plants,  parts  are  entindy  absent  which  analogy  would  lead  us 
to  expect  to  find,  and  which  are  occasionally  found  in  mon- 
strous individuals.  Thus  in  most  of  the  ijcrophulariaceoe  the 
tifth  stamen  is  utterly  aborted ;  yet  we  may  conclude  that  a 
fifth  stamen  once  existed,  for  a  rudiment  of  it  is  found  in  many 
species  of  the  family,  and  this  rudiment  occasionally  becomes 
])('rfectly  developed,  as  may  be  seen  in  the  common  snap- 
dragon. In  tracing  tlie  homologies  of  any  part  in  diflerent 
members  of  the  same  class,  nothing  is  more  common,  or  more 
necessary,  in  order  fully  to  understand  the  relations  of  the 
])arts,  than  the  discovery  of  rudiments.  This  is  well  shown  in 
llic  drawings  given  hy  Owen  of  the  bones  of  the  leg  of  the 
horse,  ox,  and  rhinocero.s. 

It  is  an  important  fact  that  rudimentary  organs,  such  as 
teeth  in  the  upper  jaws  of  whales  and  ruminants,  can  often 
1)e  detected  in  the  embryo,  but  afterward  wholly  disappear.  It 
is  also,  I  believe,  a  universal  rule,  tliat  a  rudimentary  part  is 
of  greater  size  relatively  to  the  adjoining  parts  in  the  embryo, 
than  in  the  adult ;  so  that  the  organ  at  this  early  age  is  less 
rudimentary,  or  even  cannot  l)e  said  to  be  in  any  degree  rudi- 
mentary. Hence  rudimentary  organs  in  the  adult  are  often 
said  to  have  retained  their  embryt)nic  condition. 

I  have  now  given  the  leading  facts  witli  respect  to  rudi- 
mentary organs.  In  reflecting  on  them,  every  one  must  be 
struck  with  astonishment :  for  the  same  reasoning  power  which 
tells  us  that  most  parts  and  organs  are  e.\(iuisitely  adai)ted  for 
C{>rtain  purposes,  tells  us  with  e([ual  plainness  that  these  rudi- 
mentary or  atrophied  organs  are  imperfect  and  useless.  In 
works   o;i    n:iiu!Ml   liislnrv,  rudimentary  organs  arc  generally 


408  RUDIMENTAIJY,   ATKOPUIED,  Cii.vr.  XIII. 

said  to  have  been  created  "  for  the  sake  of  synnnetry,'"  or  in 
order  "  to  complete  the  scheme  of  Nature."  But  this  is  not  an 
explanation,  merely  a  restatement  of  the  fact.  Nor  is  it  con- 
sistent Avith  itself :  thus  the  boa-constrictor  has  rudiments  of 
hind-limbs  and  of  a  pelvis,  and  if  it  be  said  that  these  bones 
have  been  n^taincd  "  to  complete  the  scheme  of  Nature,"  why, 
as  Prof.  Wcismann  asks,  have  they  not  been  retained  by 
other  snakes,  which  do  not  possess  even  a  vestige  of  these 
same  bones  ?  What  would  be  thought  of  an  astronomer  who 
niuintained  that  the  satellites  revolve  in  elliptic  courses  round 
their  planets  "for  the  sake  of  symmetry,"  because  the  planets 
thus  revolve  round  the  sun  ?  An  eminent  physiologist  ac- 
counts for  the  j)rescneo  of  rudimentary  organs,  by  supposing 
that  they  serve  to  excrete  matter  in  excess,  or  matter  injurious 
to  the  system ;  but  can  we  sujipose  that  the  minute  papilla, 
Avhich  often  represents  the  pistil  in  male  flowers,  and  wliich  is 
formed  of  mere  cellular  tissue,  can  thus  act  ?  Can  we  suppose 
that  rudimentary  teeth,  which  ai'e  subsequently  absorbed,  are 
beneficial  to  the  rapidly-growing  embryonic  calf  by  removing 
matter  so  precious  as  phosphate  of  lime  ?  When  a  man's  fin- 
gers have  been  amputated,  imperfect  nails  have  been  known  to 
appear  on  the  stumps,  and  I  could  as  soon  believe  that  these 
vestiges  of  nails  have  been  developed  in  order  to  excrete  homy 
matter,  as  that  the  rudimentary  nails  on  the  fin  of  the  mana- 
tee have  been  developed  for  this  same  purpose. 

On  the  view  of  descent  Avith  modification,  the  origin  of 
rudimentary  organs  is  simple.  We  have  plenty  of  cases  of 
rudimentary  organs  in  our  domestic  productions — as  the  stump 
of  a  tail  in  tailless  breeds — the  vestige  of  an  ear  in  earless 
breeds  of  sheep — the  reappearance  of  minute  dangling  horns 
in  hornless  breeds  of  cattle,  more  especially,  according  to 
Youatt,  in  young  animals — and  the  state  of  the  whole  flower 
in  the  cauliflower.  We  often  see  rudiments  of  various  parts 
in  monsters.  But  I  doubt  whether  any  of  these  cases  throw 
light  on  tlie  origin  of  rudimentary  organs  in  a  state  of  nature, 
further  than  by  showing  that  rudiments  can  be  produced ;  for 
I  doubt  whether  species  under  Nature  ever  undergo-  abrupt 
changes.  I  believe  that  disuse  has  been  the  main  agency  ; 
that  it  has  led  in  successive  generations  to  the  gradual  redut»- 
tion  of  various  organs,  imtil  tliey  have  become  rudimentary — 
as  in  the  case  of  tlie  eyes  of  animals  inhabiting  dark  caverns, 
and  of  the  wings  of  birds  iidiabiting  oceanic  islands,  which 
h:ive  seldom  be(Mi  forced  ])y  l)e;ists  of  prey  to  take  flight,  and 


Chap.  XIII.  AND  ABORTED  ORGANS.  409 

have  ultimately  lost  tlie  power  of  flying.  Again,  an  organ 
useful  under  certain  conditions,  might  become  injurious  under 
others,  as  with  tlic  wings  of  beetles  living  on  small  and  ex- 
posed islands;  and  in  tliis  case  natural  selection  would  con- 
tinue slowly  to  reduce  the  organ,  until  it  was  rendered  harm- 
less and  ruihmentary. 

Any  change  in  structure,  and  function,  which  can  be  ef- 
fected by  insensibly  small  steps,  is  within  the  power  of  natural 
selection ;  so  that  an  organ  rendered,  through  changed  haliits 
of  life,  useless  or  injurious  for  one  purpose,  might  he  modified 
and  used  for  another  purpose.  An  organ  might,  also,  be 
retained  for  one  alone  of  its  f(jrmer  functions.  An  organ,  ori- 
ginally formed  by  the  aid  of  natural  selection,  when  rendered 
useless,  may  well  be  vai-iable,  for  its  variations  can  no  longer  be 
checked  by  natural  selection.  At  whatever  period  of  life  either 
disuse  or  selection  reduces  an  organ,  and  this  will  generally  1)C 
when  the  being  has  come  to  maturity  and  has  to  exert  its  full 
powers  of  action,  the  principle  of  inheritance  at  corresponding 
ages  will  reproduce  the  organ  in  its  reduced  state  at  the  same 
mature  age,  but  will  seldom  affect  it  in  the  cmbrj-o.  Thus  we 
can  understand  the  greater  size  of  rudimentary  organs  in  the 
embryo  relatively  to  its  other  parts,  and  their  lesser  relative 
size  in  the  adult.  But  if  each  step  of  the  process  of  reduction 
wore  to  be  inlierited,  not  at  a  corresponding  age,  but  at  a  Aery 
early  perioil  of  life,  the  rudimentary  part  would  tend  to  be 
whoUv  lost,  and  we  should  have  a  case  of  complete  abortion. 
Tlie  principle,  also,  of  the  economy  of  organization,  explained 
in  a  former  chapter,  by  which  the  materials  forming  any  part, 
if  not  useful  to  tlie  possessor,  will  be  saved  as  for  as  is  pos- 
sible, may  often  have  come  into  play,  and  aided  in  the  entire 
obliteration  of  a  rudimentary  organ. 

As  the  presence  of  rudimentary  organs  is  thus  due  to  the 
tendency  in  every  part  of  the  organization,  which  has  long 
existed,  to  be  inherited — we  can  understand,  on  the  genealo- 
gical view  of  classification,  how  it  is  that  systematists  have 
found  rudimentary  parts  as  useful  as,  or  even  sometimes  more 
useful  than,  parts  of  high  ])hysiological  importance.  Kudimen- 
tary  organs  may  be  comjiared  with  the  letters  in  a  word,  still 
retained  in  the  spelling,  but  become  useless  in  the  pronuncia- 
tion, but  which  serve  as  a  clew  for  its  derivation.  On  the  view 
of  descent  with  modilication,  we  may  conclude  that  the  exist- 
I'uce  of  organs  in  a  rudimentary,  imperfect,  and  useless  condi- 
tion, or  quite  al)orled,  far  from  presenting  a  strange  diilicultv, 
18 


410  SUMMARY.  Cuap.  XIII. 

as  they  assuredly  do  on  the  ordinary  doctrine  of  creation^ 
might  even  have  been  anticipated  in  accordance  with  the  ^'iews 
here  explained. 

Summary. 

In  this  chapter  I  have  attempted  to  show  that  the  arrange- 
ment of  all  organic  beings  throughout  all  time  in  group  under 
group — that  the  nature  of  the  relationship,  by  which  all  living 
and  extinct  organisms  are  united  by  complex,  radiating,  and 
circuitous  lines  of  affinities  in  a  few  grand  classes — the  rules 
followed  and  the  difficulties  encountered  by  naturalists  in  their 
classifications — the  value  set  upon  characters,  if  constant  and 
prevalent,  whether  of  high  or  the  most  trifling  importance,  or, 
as  with  rudimentary  organs,  of  no  importance — the  wide  oppo- 
sition in  value  between  analogical  or  adaptive  characters,  and 
characters  of  true  aflinity,  and  other  such  rules — all  naturally 
follow  if  we  admit  the  common  parentage  of  allied  forms,  to- 
gether with  their  modification  through  natural  selection,  with 
its  contingencies  of  extinction  and  divergence  of  character. 
In  considering  tliis  view  of  classification,  it  should  be  borne  in 
mind  that  the  element  of  descent  has  been  universally  used  in 
ranlcing  together  the  sexes,  ages,  dimoi-jihic  forms,  and  acknowl- 
edged varieties  of  the  same  species,  however  different  they 
may  be  in  structure.  If  we  extend  the  use  of  this  element  of 
descent — the  one  certainly  known  cause  of  similarity  in  or- 
ganic beings — we  shall  understand  what  is  meant  by  the  Nat- 
ural System :  it  is  genealogical  in  its  attempted  arrangement, 
with  the  grades  of  acquired  difference  marked  by  the  terms, 
varieties,  species,  genera,  families,  orders,  arid  classes. 

On  this  same  view  of  descent  with  modification,  all  the 
great  facts  in  Morphology  become  intelligible — whether  we 
look  to  the  same  pattern  displayed  by  the  different  species  of 
the  same  class  in  their  homologous  organs,  to  whatever  pur- 
pose applied  ;  or  to  the  homologous  parts  in  each  individual 
animal  and  plant. 

On  this  principle  of  successive  slight  variations,  not  neces- 
sarily or  generally  supervening  at  a  very  early  period  of  life, 
and  being  inherited  at  a  corresponding  period,  we  can  under- 
stand the  great  leading  facts  in  Embryology ;  namely,  the 
close  resemblance  in  the  individual  embryo  of  the  parts  which 
are  homologous,  and  which  when  matured  become  widely  dif- 
ferent in  structure  and  function  ;  and  the  resemblance  in  allied 
though   very  distinct   species  of  their  homologous   parts  or 


CuAP.  XIII.  SUMMARY.  411 

organs,  though  fitted  in  the  adult  state  for  purposes  as  differ- 
ent as  is  possible.  Liirv:i3  are  active  embryos,  ^vhich  have 
been  specially  modified  in  a  greater  or  less  degree  in  relation 
to  their  habits  of  life,  with  their  modifications  inherited  at  a 
corresponding  age.  On  these  same  principles — and  bearing  in 
mind  that,  when  organs  are  reduced  in  size,  either  from  disuse 
or  through  natural  selection,  it  will  generally  be  at  that  period 
of  life  when  the  being  has  to  provide  for  its  own  wants,  and 
bearing  in  mind  how  strong  is  the  force  of  inheritance — the 
occurrence  of  rudiment;iry  organs  might  even  have  been  anti- 
cipated. The  importance  of  embryological  characters  and  of 
rudimentary  organs  in  classification  is  intelligible,  on  the  view 
that  a  natural  arrangement  must  be  genealogical. 

Final]}-,  the  several  classes  of  facts  which  have  been  con- 
sidered in  this  chapter,  seem  to  me  to  proclaim  so  plainly  that 
the  innumerable  species,  genera,  and  families,  with  which  this 
world  is  peopled,  are  all  descended,  each  within  its  own  class 
or  group,  from  connnon  parents,  and  have  all  been  modified  in 
the  course  of  descent,  that  I  should  without  hesitation  adopt 
this  view,  even  if  it  were  unsupported  by  any  other  facts  or 
arguments. 


412  RECAPITULATION.  Cillt.  XIV. 


CHAPTER  XIV. 

RECAPITULATIOX   AND   CONCLUSION. 

Recapitulation  of  the  Ohjoctiors  to  the  Tlieoiy  of  Natural  Selection— Reeapitulafion 
of  the  General  and  Special  Circumstances  in  its  favor— Causes  of  the  General  Be- 
lief in  the  Immutability  of  Species— How  far  the  Theory  of  Natural  Selection  may 
l>o  extended— ElTccts  of  its  Adoption  on  the  Study  of  Natural  History— Concluci- 
ing  Kemarks. 

As  this  whole  volume  is  one  long  argument,  it  may  be  con- 
venient to  the  reader  to  have  the  leading  facts  and  inferences 
briefly  recapitulated. 

That  many  and  serious  objections  ma}-  be  advanced  against 
the  theory  of  descent  with  modification  through  natural  selec- 
tion, I  do  not  den}'.  I  have  endeavored  to  give  to  them  their 
full  force.  Nothing  at  first  can  appear  more  difficult  to  be- 
lieve than  that  the  more  complex  organs  and  instincts  have 
])ocn  perfected,  not  by  means  superior  to,  though  analogous 
witli,  human  reason,  but  by  the  accumulation  of  innumerable 
slight  variations,  each  good  for  the  individual  possessor.  Nev- 
ertheless, this  difficulty,  though  appearing  to  our  imagination 
insuperably  great,  cannot  be  considered  real  if  we  admit  the 
following  propositions,  namely,  that  all  ]>arts  of  the  organiza- 
tion and  instincts  offer,  at  least,  individual  differences — that 
there  is  a  struggle  for  existence  leading  to  the  preservation  of 
profitable  deviations  of  structure  or  instinct — and,  lastly,  that 
gradations  in  the  state  of  perfection  of  each  organ  may  have 
existed,  each  good  of,its  Idnd.  The  truth  of  these  propositions 
cannot,  I  think,  be  disputed. 

It  is,  no  doubt,  extremely  difficult  even  to  conjecture  by 
what  gradations  many  structures  have  been  perfected,  more 
especially  among  broken  and  failing  groups  of  organic  beings, 
which  have  suffered  much  extinction  ;  but  we  see  so  many 
strange  gradations  in  Nature,  that  Ave  ought  to  be  extremely 
cautious  in  saying  that  any  organ  or  instinct,  or  the  whole 
structure,  could  not  have  arrived  at  its  present  state  by  many 


CMiAP.  XIV.  RECAPITULATION.  413 

graclutited  .steps.  There  are,  it  must  be  admitted,  cases  of 
special  diiriculty  oppo.se(l  to  tlie  theory  of  natural  selection ; 
and  one  of  the  most  curious  of  tlicse  is  the  existence  of  two  or 
three  defined  castes  of  workers  or  sterile  female  ants  in  the 
same  community ;  but  I  have  attempted  to  show  how  these 
dilKculties  can  be  mastered. 

With  respect  to  the  almost  universal  sterility  of  Species 
when  first  crossed,  which  forms  so  remarkable  a  contrast  with 
the  almost  universal  fertility  of  varieties  when  crossed,  I  must 
refer  the  reader  to  the  recapitulation  of  tlie  facts  given  at  the 
end  of  the  eighth  chapter,  which  seem  to  me  conclusively  to 
show  that  this  sterility  is  no  more  a  special  endowment  than 
is  the  incapacity  of  two  distinct  trees  to  be  grafted  together; 
but  that  it  is  incidental  on  differences  confined  to  the  repro- 
ductive systems  of  the  intercrossed  species.  We  see  the  truth 
of  this  conclusion  in  the  vast  difference  in  the  results  of  cross- 
ing the  same  two  species  reciprocall}- — that  is,  when  one 
species  is  first  used  as  the  father  and  then  as  the  mother : 
analogy  from  the  consideration  of  dimorphic  and  triraorphic 
plants  clearly  leads  to  tlic  same  conclusion,  for  when  the  forms 
are  illegitimately  united,  they  yield  few  or  no  seed,  and  their 
offspring  arc  more  or  less  sterile  ;  and  these  forms  of  the  same 
undoulited  species  dlfler  in  no  respect  from  each  other  except 
in  their  reproductive  organs  and  functions. 

Although  the  fertility  of  varieties  when  intercrossed  and  of 
their  mongrel  offspring  has  been  asserted  by  so  many  authors 
U)  1)0  universal,  this  cannot  be  considered  correct  after  the  fiicts 
given  on  the  authority  of  Gartner  and  Kijlreuter.  Nor  is  the 
very  general  fertility  of  varieties,  when  crossed,  surprising, 
when  we  remember  that  it  is  not  likely  that  their  reproductive 
sj-stems  should  have  been  profoundly  modified.  Moreover, 
most  of  the  varieties  which  have  been  experimente(l  on  have 
been  produced  under  domestication  ;  and  as  domestication  (I 
do  not  mean  mere  confinement)  almost  certainly  tends  to  elim- 
inate sterility,  we  ought  not  to  expect  it  also  to  produce 
sterility. 

The  sterility  of  hyl)rids  is  a  different  case  from  that  of  a 
first  cross,  for  tli(»  reproductive  organs  of  hybrids  arc  more  or 
less  functionally  impotent ;  whereas  in  first  crosses,  the  organs 
of  both  species  arc  of  course  in  a  perfect  condition.  As  we 
continually  see  that  organisms  of  all  kinds  are  rendered  in 
some  degree  sterile  from  being  exposed  to  slightly-changed 
conditions,  wc  need  not  feel  surprise  at  hybrids  being  in  some 


414  RECAPITULATION.  Cuap.  XIV. 

(lep^ree  sterile,  for  their  constitutions  can  hardly  fail  to  bo  dis- 
turbed from  beinf^  compounded  of  two  distinct  organizations  ; 
but  -whether  this  is  the  true  cause  of  their  sterility  I  will  not 
pretend  to  decide.  The  above  parallelism  is  supported  by 
another  parallel,  but  directly  opposite,  class  of  facts,  namely, 
that  the  vig'or  and  fertility  of  all  organic  beings  are  increased 
by  slight  changes  in  their  conditions  of  life,  and  that  the 
oifspring  of  slightly-modified  forms  or  varieties  when  crossed 
acquire  increased  vigor  and  fertility.  So  that,  on  the  one 
hand,  a  considerable  change  in  tlie  conditions  of  life  and  crosses 
between  greatly-modified  forms,  lessen  fertility;  and,  on  the 
other  hand,  lesser  changes  in  the  conditions  of  life  and  crosses 
between  less-modified  forms,  increase  fertility. 

Turning  to  geographical  distribution,  the  difficulties  en- 
countered on  the  theory  of  descent  with  modification  are  seri- 
ous enough.  All  the  individuals  of  the  same  species,  and  all 
the  species  of  the  same  genus,  or  even  higher  group,  must  have 
descended  from  common  parents;  and  therefore,  in  however 
distant  and  isolated  parts  of  the  world  they  may  now  be  found, 
they  must  in  the  course  of  successive  generations  have  travelled 
from  some  one  point  to  all  the  others.  We  are  often  wholly 
unable  even  to  conjecture  how  this  could  have  been  effected. 
Yet,  as  we  have  reason  to  believe  that  some  species  have 
retained  the  same  specific  form  for  very  long  periods  of  time, 
immensely  long  as  measured  by  years,  too  much  stress  ought 
not  to  be  laid  on  the  occasional  wide  diffusion  of  the  same  spe- 
cies ;  for  during  very  long  periods  there  will  always  be  a  good 
chance  for  wide  migration  by  many  means.  A  broken  or  in- 
terrupted range  may  often  be  accounted  for  by  the  extinction 
of  the  species  in  the  intermediate  regions.  It  cannot  be  de- 
nied that  Ave  arc  as  yet  very  ignorant  of  the  full  extent  of  the 
various  climatal  and  geographical  changes  which  have  affected 
the  earth  during  modern  periods;  and  such  changes  may  obvi- 
ously have  facilitated  migration.  As  an  exam])le,  I  have  at- 
tempted to  show  how  potent  has  been  the  influence  of  the 
Glacial  period  on  the  distribution  of  the  same  and  of  allied 
species  throughout  the  world.  We  are  as  yet  profoundly 
ignorant  of  the  many  occasional  means  of  transport.  With 
respect  to  distinct  species  of  the  same  genus  inhabiting  distant 
and  isolated  regions,  as  the  process  of  modification  has  neces- 
sarily been  slow,  all  the  means  of  migration  will  have  been 
possible    during   a    very  long   period ;  and    consequently  the  ■ 


Chap.  XIV.  RECAPITULATIOiN.  4I5 

difBculty  of  the  wide  diffusion  of  tlic  species  of  the  same  genus 
is  in  some  def^ree  lessened. 

As  uccording'  to  the  theory  of  natural  selection  an  intermi- 
nable number  of  intermediate  forms  must  have  existed,  linking* 
together  all  the  species  in  each  group  by  gradations  as  fine  as 
are  our  [jrescnt  varieties,  it  may  be  asked,  Why  do  v,'o  not 
see  these  linking  forms  all  around  us  ?  Wliy  are  not  all  organ- 
ic beinfTS  blended  tos:ether  in  an  inextricable  chaos  ?  AVith 
respect  to  existing  forms,  we  should  remember  that  we  have 
no  right  to  expect  (excepting  in  rare  cases)  to  discover  directhj 
connecting  links  between  them,  but  only  between  each  and 
some  extinct  and  supplanted  form.  Even  on  a  Avide  area, 
which  has  during  a  long  period  remained  continuous,  and  of 
which  the  climate  and  other  conchtions  of  life  change  insensibly 
in  proceeiling  fi'om  a  district  occupied  by  one  species  into 
another  district  occupied  by  a  closely-allied  species,  we  have 
HO  just  right  to  expect  often  to  find  intermediate  varieties  in 
the  intermediate  zone.  For  we  have  reason  to  believe  that 
only  a  few  species  of  a  genus  ever  imdergo  change  ;  the  other 
species  becoming  utterly  extinct  and  leaving  no  modified  pro- 
geny. Of  the  species  which  do  change,  only  a  few  Avithin  the 
same  country  change  at  the  same  time  ;  and  all  modifications 
are  slowly  effected.  I  have  also  shoAvn  that  the  intermediate 
varieties  which  prcjbably  at  first  existed  in  the  intermediate 
zones,  would  be  liable  to  be  supplanted  by  the  allied  forms  on 
either  hand;  for  the  latter,  from  existing  in  greater  numbers, 
would  generally  be  modified  and  improved  at  a  quicker  rate 
than  the  intermediate  varieties,  which  existed  in  lesser  num- 
bers ;  so  that  the  intermediate  varieties  Avould,  in  the  long- 
run,  be  supplanted  and  exterminated. 

On  this  doctrine  of  the  extermination  of  an  infinitude  of 
connecting  links,  between  the  living  and  extinct  inhabitants 
of  the  Avorld,  and  at  each  succcssIa'C  period  betAA'cen  the  ex- 
tinct and  still  older  species,  Avhy  is  not  every  geological  forma- 
tion charged  Avith  such  links  ?  Why  does  not  every  collection 
of  fcjssil  remains  afford  plain  evidence  of  the  gradation  and 
mutation  of  the  forms  of  life?  Although  geological  research 
has  undoubtedly  rcA'caled  the  former  existence  of  many  links, 
bringing  numerous  forms  of  life  much  closer  together,  it  does 
not  yield  the  infinitely  many  fine  gradations  between  i)ast  and 
present  species  required  on  the  theory  ;  and  this  is  the  most 
obvious  of  the  many  objections  Avhich  may  be  urged  against  it. 
Why,  again,  do  Avhole  groups  of  allied  sjiecies  apj)car,  though 


41G  EECAl'ITULATION.  Chap.  XIV. 

this  appearance  is  often  false,  to  have  come  in  suddenly  on  the 
successive  geological  stages '?  Although  we  now  know  that 
organic  beings  appeared  on  this  globe,  at  a  period  incalculably 
remote,  long  befc^re  the  lo^vest  bed  of  the  Cambrian  system  was 
deix)sited,  why  do  we  not  lind  beneath  this  system  great  piles  of 
strata  stored  with  the  remains  of  the  progenitors  of  the  Cam- 
brian fossils  ?  For  on  tlic  theory  such  strata  must  somewhere 
have  been  deposited  at  these  ancient  and  utterly  unknown 
epochs  in  the  world's  history. 

I  can  answer  these  ciuestions  and  olijcctions  only  on  the 
supposition  that  the  geological  record  is  far  more  imperfect 
than  most  geologists  believe.  The  number  of  s]x;cimens  in  all 
our  museums  is  absolutely  as  nothing  compared  with  the 
countless  generations  of  countless  species  wliich  have  certainly 
existed.  The  parent-form  of  any  two  or  more  sjx^cies  would 
not  be  in  all  its  characters  directly  intermediate  between  its 
modified  odspring,  any  more  than  the  rock-pigeon  is  directly 
intermediate  in  crop  and  tail  between  its  descendants  the 
pouter  and  fantail  pigeons.  We  should  not  l>e  able  to  recog- 
nize a  species  as  the  parent  of  another  and  modified  species,  if 
we  were  to  examine  both  ever  so  closely,  unless  we  possessed 
most  of  the  intermediate  links  ;  and  owing  to  the  imjxjrfection 
of  the  geological  record,  we  have  no  just  right  to  expect  to 
find  so  many  hnks.  If  two  or  three,  or  even  more  linking 
forms  were  discovered,  they  would  simply  be  ranked  as  so 
many  new  species,  more  especially  if  found  in  different  geolo- 
gical sub-stages,  let  their  differences  be  ever  so  slight.  Nu- 
merous existing  doubtful  forms  could  be  named  which  are  prob- 
ably varieties ;  but  who  will  pretend  that  in  future  ages  so 
man}-  fossil  links  Avill  be  discovered,  that  naturalists  will  be 
able  to  decide  whether  or  not  these  doubtful  forms  ought  to  be 
called  varieties  ?  Only  a  small  portion  of  the  world  has  been 
geologically  explored.  Only  organic  beings  of  certain  classes 
can  be  preserved  in  a  fossil  condition,  at  least  in  any  great 
i\uinl)er.  Many  species  when  once  formed  never  undergo  any 
further  change,  but  become  extinct  without  leaving  modified 
descendants ;  and  the  periods,  during  which  species  have  un- 
dergone modification,  though  long  as  measured  by  years,  have 
])r()l)ably  been  short  in  comparison  with  the  periods  during 
which  tliey  have  retained  the  same  fonn.  It  is  the  dominant 
and  widely-ranging  species  which  vary  most  frequently  anil  vary 
most,  and  varieties  are  often  at  first  local — both  clauses  render- 
ing the  discovery  of  intermediate  links  in  any  one  formation 


Chap.  XIV.  RECAPITULATION.  417 

less  likely.  LckmI  varieties  will  not  spread  into  other  and  dis- 
tant reg^ions  until  they  are  considerably  modilied  and  improved  ; 
and  when  they  have  spread,  and  are  discovered  in  a  ji^eological 
formation,  they  will  appear  as  if  silddenly  created  there,  and 
will  be  simply  classed  as  new  species.  Most  formations  have 
been  intermittent  in  their  accumulation;  and  their  duration 
has  probably  been  shorter  than  the  average  duration  of  spe- 
cific forms.  Successive  formations  are  in  most  cases  separated 
from  each  other  by.  blank  intervals  of  time  of  great  length ;  for 
fossiliferous  formations  thick  enough  to  resist  future  degrada- 
tion can  as  a  general  rule  be  accumulated  only  where  much 
sediment  is  deposited  on  the  subsiding  bed  of  the  sea.  During 
the  alternate  periods  of  elevation  and  of  stationary  level  the 
recortl  will  generally  be  blank.  During  these  latter  periods 
tliere  will  i^robably  be  more  variability  in  the  forms  of  life ; 
during  periods  of  subsidence,  more  extinction. 

Witii  respect  to  the  absence  of  strata  rich  in  fossils  beneath 
the  Caml)rian  formation,  I  can  recur  only  to  the  hypotliesis 
given  in  the  ninth  chajiter.  That  the  geological  record  is  im- 
perfect all  will  admit ;  but  that  it  is  imperfect  to  the  degree  re- 
quired l)y  our  theory,  few  will  be  inclined  to  admit.  If  we 
look  to  long-enough  intervals  of  time,  geology  plainly  declares 
that  species  have  all  changed ;  and  they  have  changed  in  the 
manner  required,  for  they  have  changed  slowly  and  in  a  grad- 
uated manner.  We  clearly  see  this  in  the  fossil  remains  from 
consecutive  formations  invariably  being  much  more  closely  re- 
lated to  each  other  than  are  the  fossils  from  widely-separated 
formations. 

Such  is  the  sum  of  the  several  chief  objections  and  dilhcul- 
ties  which  may  justly  be  urged  against  the  theory  ;  and  1  have 
now  briefly  recapitulated  the  answers  and  explanations  which 
can  be  given.  I  have  felt  these  diiliculties  far  too  heavily  dur- 
ing many  years  to  doubt  their  weight.  But  it  deserves  espe- 
cial notice  that  the  more  important  objections  relate  to  ques- 
tions on  which  we  are  confessedly  ignorant ;  nor  do  we  know 
how  ignorant  we  are.  AVe  do  not  know  all  the  possible  tran- 
sitional gradations  between  the  simplest  and  the  most  perfect 
organs;  it  cannot  be  pretendecl  that  we  know  all  the  varied 
means  of  Distril)uti()n  during  the  long  lapse  of  years,  or  that 
we  know  how  imperfect  the  Geological  Kecord  is.  ^ferious  as 
these  several  objections  are,  in  \uy  judgment  they  are  not 
suflicient  to  overthrow  the  theory  of  descent  with  subsequent 
modification. 


418  RECAPITULATION.  Chap.  XIV. 

Now  let  us  lum  to  the  other  side  of  the  argument.  Under 
domestication  Ave  see  much  variability,  caused,  or  at  least  ex- 
cited, liy  changed  conditions  of  life.  This  variability  is  gov- 
erned by  many  complex  laws — by  correlation,  by  use  and  dis- 
use, and  by  the  definite  action  of  the  surrounding  conditions. 
There  is  much  difficulty  in  ascertaining  hoAV  largely  our  do- 
mestic productions  have  been  modified ;  but  we  may  safely  in- 
fer that  the  amount  has  been  large,  and  that  modifications  can 
be  inherited  for  long  periods.  As  long  as  the  conditions  of 
life  remain  the  same,  we  have  reason  to  believe  that  a  modifi- 
cation, Avhich  has  already  been  inherited  for  many  generations, 
may  continue  to  be  inherited  for  an  almost  infinite  number  of 
generations.  On  the  other  hand,  Ave  haAO  evidence  that  vari- 
ability, AA-hen  it  has  once  come  into  play,  does  not  cease  under 
domestication  for  a  very  long  period;  for  noAV  A'arieties  are 
still  occasionally  produced  by  our  oldest  domesticated  produc- 
tions. 

Man  does  not  actually  produce  variability ;  he  only  unin- 
tentionally exposes  organic  beings  to  ncAV  conditions  of  life, 
and  then  Nature  acts  on  the  organization,  and  causes .A'ari abil- 
ity. But  man  can  and  docs  select  the  A-ariations  given  to  him 
by  Nature,  and  thus  accumulate  them  in  any  desired  manner. 
lie  thus  adapts  animals  and  plants  for  his  OAvn  benefit  or 
pleasure.  He  may  do  this  methodically,  or  he  may  do  it  un- 
consciously, by  preserving  the  indiA'iduals  most  useful  or  pleas- 
ing to  hini  Avithout  any  intention  of  altering  the  breed.  It  is 
certain  that  he  can  largely  influence  the  character  of  a  breed 
Ijy  selecting,  in  each  successive  generation,  individual  differ- 
ences so  slight  as  to  be  inap{)reciable  except  by  an  educated 
eye.  This  process  of  selection  has  been  the  great  agency  in 
f  lie  formation  of  the  most  distinct  and  useful  domestic  breeds. 
That  many  breeds  produced  by  man  have  to  a  large  extent  the 
character  of  natural  species,  is  shown  by  the  inextricable 
doubts  AA'hether  many  of  them  are  Aarietics  or  aboriginally  dis- 
tinct species. 

There  is  no  obvious  reason  why  the  principles  Avhich  have 
acted  so  cfficientl}^  under  domestication  should  not  act  under 
Nature.  In  the  survival  of  favored  individuals  and  races,  dur- 
ing the  constantly-recurrent  Struggle  for  Existence,  Ave  see  a 
jKnverful  and  ever-acting  form  of  Selection.  The  struggle  for 
existence  inevitably  follows  from  the  high  geometrical  ratio  of 
increase  Avhich  is  common  to  all  organic  beings.  This  high 
rate  of  increase  is  proved  by  calculation — l)y  the  rapid  increase 


CiiAr.  XIV.  RECAPITULATION.  419 

of  many  animals  and  plants  during  a  succession  of  peculiar 
seasons,  and  when  naturalized  in  a  new  country.  More  indi- 
viduals are  born  than  can  possibly  survive.  A  grain  in  the 
balance  may  determine  which  individuals  shall  live  and  which 
shall  die — which  variety  or  species  shall  increase  in  number, 
and  which  shall  decrease,  or  linally  become  extinct.  As  the 
individuals  of  the  same  species  come  in  all  respects  into  the 
closest  competition  with  each  other,  the  struggle  will  gener- 
ally be  most  severe  between  them ;  it  will  be  almost  equally 
severe  between  the  varieties  of  the  same  species,  and  next  in 
severity  between  the  species  of  the  same  genus.  On  the  other 
hand,  the  struggle  will  often  be  very  severe  between  beings  re- 
mote in  the  scale  of  nature.  The  slightest  advantage  in  cer- 
tain individuals,  at  any  age  or  during  any  season,  over  those 
with  which  they  come  into  competition,  or  better  adaptation 
in  however  slight  a  degree  to  the  surrounding  physical  condi- 
tions, will  turn  tlic  balance. 

With  animals  having  separated  sexes  there  will  be  in  most 
cases  a  struggle  between  the  males  for  the  possession  of  the 
females.  The  most  vigorous  males,  or  those  which  have  most 
successfully  struggled  with  then'  conditions  of  life,  will  gener- 
ally leave  most  progeny.  But  success  will  often  depend  on 
the  males  having  special  weapons,  or  means  of  defence,  or 
charms ;  and  a  slight  advantage  Avill  lead  to  victory. 

A3  geology  plainly  proclaims  that  each  land  has  under- 
gone great  physical  changes,  we  might  have  expected  to  find 
that  organic  beings  have  varied  under  Nature,  in  the  same  way 
as  they  have  varied  under  domestication.  And  if  there  be  any 
variability  under  Nature,  it  would  be  an  unaccountable  fiict  if 
natural  selection  did  not  come  into  play.  It  has  often  been 
asserted,  but  the  assertion  is  incapable  of  proof,  that  the 
amount  of  variation  under  Nature  is  a  strictly  limited  fjuantity. 
i\Ian,  though  acting  on  external  characters  alone  and  often 
capriciously,  can  produce  w'ithin  a  short  peritxl  a  great  result 
by  adding  up  mere  individual  differences  in  his  domestic  pro- 
ductions; and  every  one  admits  that  species  present  individual 
difFerences.  15ut,  besides  such  dill'erences,  all  naturalists  admit 
that  varieties  exist,  which  are  considered  sulliciently  distinct 
to  be  worthy  of  record  in  systematic  works.  No  one  has 
drawn  any  clear  distinction  between  individual  dilVerences  and 
slight  varieties  ;  or  between  more  plainly-marked  varieties 
and  sub-species,  and  species.  f)n  separate  contincMits,  and  on 
dilFercnt  parts  of  the  same  continent  when  divided  hy  l)arriers 


420  RECAPITULATION.  Chap.  XIV. 

of  any  kind,  and  on  outlying  islands,  Mliat  a  multitude  of 
forms  exist,  ■which  some  experienced  naturalists  rank  as  vari- 
eties, others  as  geographical  races  or  sub-species,  and  others 
as  distinct  though  closely-allied  species  ! 

If,  then,  animals  and  plants  do  vary,  let  it  be  ever  so  little 
or  so  slowlv,  why  should  we  doubt  that  the  variations  or  in- 
dividual dill'erences,  which  are  in  any  way  beneficial,  would  be 
preserved  and  accumulated  through  natural  selection,  or  the 
survival  of  tlie  fittest  ?  If  man  can  by  patience  select  varia- 
tions useful  to  him,  Avhy,  under  changing  and  complex  condi- 
tions of  life,  should  not  variations  useful  to  Nature's  living 
products  often  arise,  and  be  preserved  or  selected  ?  What 
limit  can  be  put  to  this  power,  acting  during  long  ages  and 
rigidly  scrutinizing  the  whole  constitution,  structure,  and 
habits  of  each  creature — fiworing  the  good  and  rejecting  the 
bad  ?  I  can  see  no  limit  to  this  power,  in  slowly  and  beauti- 
fully adapting  each  form  to  the  most  complex  relations  of  life. 
The  theory  of  natural  selection,  even  if  we  looked  no  further 
than  this,  seems  to  me  to  be  in  itself  probable.  I  have  already 
recapitulated,  as  fairly  as  I  could,  the  opposed  difficulties  and 
objections  :  now  let  us  turn  to  the  special  facts  and  arguments 
in  favor  of  the  theory. 

On  the  view  that  species  are  only  strongly-marked  and 
permanent  varieties,  and  that  each  species  fii-st  existed  as  a 
variety,  we  can  see  why  it  is  that  no  line  of  demarcation  can 
be  drawn  between  species,  commonly  supposed  to  have  been 
produced  by  special  acts  of  creation,  and  varieties  A\hicli  arc 
acknowledged  to  have  been  produced  by  secondary  laws.  On 
this  same  view  we  can  imderstand  how  it  is  that  in  each  region 
where  many  sjiecies  of  a  genus  have  been  produced,  and  where 
they  now  ilourish,  these  same  species  should  present  many 
\  aricties ;  for  whei'e  the  manufactory  of  species  has  been 
active,  Ave  might  expect,  as  a  general  rule,  to  find  it  still  iu 
action  ;  and  this  is  the  case  if  varieties  be  incipient  species. 
^Moreover,  the;  species  of  the  larger  genera,  which  ailord  the 
greater  number  of  varieties  or  incipient  species,  retain  to  a 
certain  degree  the  character  of  varieties ;  for  they  dilfer  froiu 
cacli  other  by  a  less  amount  of  dilference  than  do  the  species 
of  smaller  genera.  The  closely-allied  species  also  of  the  larger 
genera  ap])arently  have  restricted  ranges,  and  in  their  affinities 
tliey  are  clustered  in  little  groups  round  other  species — in  both 
of  Avhich  respects  they  resemble  varieties.     These  are  strange 


Chap.  XIV.  RECAPITULATION.  421 

relations  on  the  view  that  each  species  was  independently 
created,  but  are  intelligible  if  each  existed  fust  as  a  variety. 

As  each  species  tends  by  its  jji:eoinelrical  ratio  of  rei)roduc- 
tion  to  increase  inordinately  in  number ;  and  as  the  modified 
descendants  of  each  species  will  be  enabled  to  increase  by  so 
much  the  more  as  they  become  diversified  in  habits  and  struct- 
ure, so  as  to  be  enabled  to  seize  on  many  and  widely  diflerent 
jilaces  in  the  economy  of  Nature,  there  will  be  a  constant  ten- 
dency in  natural  selection  to  preserve  the  most  divergent  oft- 
spriiior  of  any  one  species.  Hence,  during  a  long-continued 
course  of  modification,  the  slight  differences,  characteristic  of 
varieties  of  the  same  species,  tend  to  be  augmented  into  the 
greater  differences  characteristic  of  the  species  of  the  same 
genus.  New  and  improved  varieties  will  inevitably  supplant 
and  exterminate  the  older,  less  improved,  and  inteimediate 
varieties  ;  and  thus  species  are  rendered  to  a  large  extent  de- 
fined and  distinct  objects.  Dominant  species  belonging  to  the 
larger  groups  within  each  class  t(>nd  to  give  birth  to  new  and 
dominant  forms  ;  so  that  each  large  group  tends  to  become 
still  larger,  and  at  the  same  time  more  divergent  in  character. 
But  as  all  groups  cannot  tlius  succeed  in  increasing  in  size,  for 
the  world  would  not  hold  them,  the  more  dominant  groups 
beat  tlie  less  dominant.  This  tendency  in  the  large  groups  to 
go  on  increasing  in  size  and  diverging  in  character,  together 
with  the  almost  inevitable  contingency  of  much  extinction,  ex- 
plains the  arrangement  of  all  the  forms  of  life,  in  groups  sub- 
ordinate to  groujis,  all  within  a  few  great  classes,  which  has 
prevailed  throughout  all  time.  This  grand  fact  of  the  group- 
ing of  all  organic  beings  under  what  is  called  the  Natural 
System,  is  utterly  inexplicable  on  the  tlieory  of  creation. 

As  natural  selection  acts  solely  by  accumulating  slight, 
successive,  favorable  variations,  it  can  produce  no  great  or  sud- 
den modification  ;  it  can  act  only  by  short  and  slow  steps. 
Hence  the  canon  of  "  Natura  iion  facit  saltum,"  which  every 
fresh  addition  to  our  knowledge!  lends  to  make  truer,  is  on 
this  theory  intelligible.  We  can  sec;  why  throughout  Nature 
the  .same  general  end  is  gained  by  an  almost  inliiiite  diversity 
of  Tneans  ;  for  every  peculiarity  when  once  acquired  is  long 
inherited,  and  structures  already  diversified  in  many  ways 
have  to  be  adapted  for  the  same  general  purpose.  AVe  can, 
in  short,  see  why  Nature  is  prodigal  in  variety,  though  nig- 
gard in  innovation.  But  why  this  .should  be  a  law  of  Nature 
if  each  species  had  been  independently  created,  no  man  can 
ex])lain. 


422  RECAPITULATION.  Cuap.  XIV. 

Many  other  facts  arc,  as  it  seems  to  me,  explicable  on  this 
theory.  How  strange  it  is  that  a  bird,  under  the  form  of 
woodj)ecker,  should  have  been  created  to  prey  on  insects  on 
the  ground ;  that  upland  geese,  which  never  or  rarely  swim, 
should  have  been  created  with  webbed  feet ;  that  a  thrush- 
like bird  should  have  been  created  to  dive  and  feed  on  sub- 
aquatic  insects ;  and  that  a  petrel  should  have  been  created 
with  the  habits  and  structure  fitting  it  for  the  life  of  an  auk ! 
— and  so  in  endless  other  cases.  But,  on  the  view  of  each 
species  constantly  trying  to  increase  in  number,  with  natural 
selection  always  ready  to  adapt  the  slowly-varying  descend- 
ants of  each  to  any  unoccupied  or  ill-occupied  place  in  Nature, 
these  facts  cease  to  be  strange,  or  might  even  have  been  an- 
ticipated. 

We  can  understand  how  it  is  that  such  harmonious  beauty 
generally  prevails  throughout  Nature.  That  there  are  excep- 
tions according  to  our  ideas  of  beauty,  no  one  will  doubt  who 
Avill  look  at  some  of  the  venomous  snakes,  at  some  fish,  and  at 
certain  hideous  bats  with  a  distorted  resemblance  to  the  hu- 
man face.  Sexual  selection  has  given  the  most  brilliant  colors 
and  other  ornaments  to  the  males,  but  sometimes  to  both  sexes 
of  many  birds,  butterflies,  and  a  few  other  animals.  With 
birds  it  has  often  rendered  the  voice  of  the  male  musical  to  the 
female,  as  well  as  to  our  ears.  Flowers  and  fruit  have  been 
rendered  conspicuous  by  gaudy  colors  in  contrast  with  the 
green  foliage,  in  order  that  the  flowers  might  be  easily  seen, 
visited,  and  fertilized  by  insects,  and  the  seeds  disseminated 
by  birds.  Lastly,  some  living  objects  have  become  beautiful 
through  mere  symmetry  of  growth. 

As  natural  selection  acts  by  competition,  it  renders  the  in- 
habitants of  each  country  perfect  only  in  relation  to  the  other 
inhabitants ;  so  that  we  need  feel  no  surprise  at  the  species  of 
an}'^  one  country,  although  on  the  ordinary  view  supposed  to 
have  been  created  and  specially  adapted  for  that  country, 
1)cing  beaten  and  suj^planted  by  the  naturalized  productions 
from  another  land.  Nor  ought  we  to  marvel  if  all  the  contriv- 
ances in  Nature  he  not,  as  far  as  we  can  judge,  absolutely  per- 
fect ;  and  if  some  of  them  be  abhorrent  to  our  ideas  of  fitness. 
We  need  not  marvel  at  the  sting  of  the  bee  when  used  against 
an  enemy  often  causing  the  bee's  own  death ;  at  drones  being 
))roduced  in  such  great  numbers  for  one  single  act,  and  being 
then  slaughtered  by  their  sterile  sisters ;  at  the  astonishing 
waste  of  pollen  by  our  fir-trees ;  at  the  instinctive  hatred  of 


Chap.  XIV.  EECAPITULATION.  423 

the  queen  bee  for  lier  own  fertile  daughters  ;  at  it  lincumoiiid:c 
fcediiifr  within  the  livin"^  bodies  of  ciiterpilhirs ;  und  ut  other 
such  cases.  The  wonder  indeed  is,  on  the  theory  of  natural 
selection,  that  more  cases  of  the  want  of  absolute  perfection 
have  not  been  observed. 

The  complex  and  little-known  laws  governing  acknowl- 
edged variations  are  the  same,  as  far  as  we  can  see,  with  the 
laws  which  have  governed  the  production  of  so-called  specific 
dillcrences.  In  both  cases  physical  conditions  seem  to  have 
produced  some  direct  and  definite  eflect,  but  how  much  we 
cannot  say.  Thus  when  varieties  enter  any  new  station,  they 
occasionally  assume  some  of  the  characters  proper  to  the  spe- 
cies of  that  station.  In  I'otli  varieties  and  species,  use  and  dis- 
use seem  to  have  produced  a  considerable  eflfect ;  for  it  is  im- 
possible to  resist  this  conclusion  when  we  look,  for  instance, 
at  the  logger-headed  duck,  which  has  wings  incajiable  of  flight, 
in  nearly  the  same  condition  as  in  the  domestic  duck;  or  when 
we  look  at  the  burrowing  tncutucu,  v.hich  is  occasionally 
l)lind,  and  then  at  certain  moles,  which  are  habitually  blind 
and  have  tlieir  eyes  cov^ercd  witli  skin ;  or  wlicn  we  look  at 
the  blind  animals  inhabiting  the  dark  caves  of  America  and 
Europe.  In  varieties  and  species  correlated  variation  seems  to 
have  played  an  im})ortant  part,  so  that  when  one  part  has 
been  modified  other  parts  have  been  necessarily  modified.  In 
both  varieties  and  species  reversions  to  long-lost  characters  oc- 
cur. How  inexplicable  on  the  theory  of  creation  is  the  occa- 
sional ajipearance  of  stripes  on  the  shoulders  and  legs  of  the 
several  species  of  the  horse-genus  and  of  their  hybrids  !  How 
simply  is  this  fact  explained  if  we  believe  that  these  species 
arc  all  descended  from  a  stri{)ed  progenitor,  in  the  same  man- 
ner as  the  several  domestic  breeds  of  the  pigeon  are  descended 
from  the  blue  and  barred  rock-pigeon  ! 

On  the  ordinary  view  of  eacli  species  having  been  iudc- 
ju'!id('iitly  created,  why  should  the  specific  characters,  or  those 
l)y  which  the  species  of  the  same  genus  diflcr  from  each  other, 
be  more  variable  than  the  generic  characters  in  which  they  all 
agree?  Why,  for  instance,  should  the  color  of  a  flower  be 
more  likel}'  to  vary  in  any  one  species  of  a  genus,  if  the  other 
species,  supposed  to  have  been  created  independently,  have 
diffenMitly-colored  flowers,  than  if  all  the  species  of  the  genus 
have  the  same  colort'd  flowers?  If  species  are  only  well- 
marked  varieties,  of  which  the  characters  have  become  in  a 
high  degree  pcnnanent,  Ave  can  understand  this  fact;  for  they 


424  KECAriTULATION.  Chap.  XIV. 

have  already  varied  since  they  branched  off  from  a  common 
progenitor  in  certain  characters,  by  which  they  have  come  to 
be  specifically  distinct  from  each  other ;  therefore  these  same 
characters  -would  be  more  likely  again  to  vary  than  the  generic 
chaiacters  Avhich  have  been  inherited  Avithout  change  for  an 
cjiormous  period.  It  is  inexplicable  on  the  theory  of  creation 
ivhy  a  part  developed  in  a  very  unusual  manner  in  any  one 
species  of  a  genus,  and  therefore,  as  we  may  naturally  infer, 
of  great  importance  to  that  species,  should  be  eminently  liable 
to  variation ;  but,  on  our  view,  this  part  has  undergone,  since 
the  several  species  branched  off  from  a  common  progenitor,  an 
luuisual  amount  of  variability  and  modification,  and  therefore 
we  might  expect  the  part  generally  ^o  be  still  variable.  But 
a  part  may  be  developed  in  the  most  unusual  manner,  like  the 
wing  of  a  bat,  and  yet  not  be  more  variable  than  any  othci 
structure,  if  the  part  be  common  to  many  subordinate  forms, 
that  is,  if  it  has  been  inherited  for  a  very  long  period ;  for  in 
this  case  it  will  have  been  rendered  constant  by  long-continued 
natural  selection. 

Glancing  at  instincts,  marvellous  as  some  are,  they  offer  no 
greater  difliculty  than  does  corporeal  structure  on  the  theory  of 
the  natural  selection  of  successive,  slight,  but  profitable  modi- 
iications.  We  can  thus  imderstand  why  Nature  moves  by 
graduated  steps  in  endowing  different  animals  of  the  same 
class  Avith  their  several  instincts,  I  have  attempted  to  show 
how  nmch  light  the  principle  of  gradation  throws  on  the  ad- 
mirable architectural  powers  of  the  hive-bee.  Habit  no  doubt 
sometimes  comes  into  play  in  modifying  instincts  ;  but  it  cer- 
tainly is  not  indispensable,  as  we  see  in  the  case  of  neuter  in- 
sects, which  leave  no  progeny  to  inherit  the  effects  of  long- 
continued  habit.  On  the  view  of  all  the  species  of  the  same 
genus  having  descended  from  a  common  parent,  and  having  in- 
herited nuich  in  common,  we  can  understand  how  it  is  that 
allied  species,  when  placed  under  widely-different  conditions 
of  life,  yet  follow  nearly  the  same  instincts ;  why  the  thrushes 
of  tropical  and  temperate  South  America,  for  instance,  line 
their  nests  with  mud  like  our  British  species.  On  the  -view  of 
instincts  having  been  slowly  acquired  through  natural  selec- 
tion, we  need  not  marvel  at  some  instincts  being  apparently 
not  ])erfect  and  liable  to  mistakes,  and  at  many  instincts  caus- 
ing other  animals  to  suffer. 

If  species  be  only  well-marked  and  permanent  varieties,  we 
can  at  once  see  why  their  crossed  offspring  should  follow  the 


CiiAi'.  XIV.  •recapitulation.  425 

same  coinph^x  laws  in  tlieir  deforces  and  kinds  of  resemblance 
to  their  parents — in  Ix'in;];'  al)sorbcd  into  each  other  by  suc- 
cessive crosses,  and  in  other  such  points — as  do  the  crossed 
oll'spring^  of  aeknowledij^ed  varieties.  Tiiis  sinuhiritj  would  be 
a  strange  fact,  if  species  liave  been  independently  created  and 
varieties  have  been  produced  thronj^h  secondary'  laws. 

If  we  admit  that  the  geolog-ical  record  is  imperfect  ia  an 
extreme  degree,  then  the  facts,  which  the  record  does  give, 
strongly  support  the  theory  of  descent  with  modification. 
New  species  have  come  on  the  stage  slowly  and  at  successive 
intervals  ;  and  the  amount  of  change,  after  equal  intervals  of 
time,  is  widely  different  in  different  groups.  The  extinction 
of  species  and  of  whole  groups  of  species,  which  has  played  so 
conspicuous  a  part  in  the  history  of  the  organic  world,  almost 
inevitably  follows  from  the  princii)le  of  natural  selection ;  for 
old  forms  are  supplanted  by  new  and  improved  forms.  Neither 
single  species  nor  groups  of  species  reappear  when  the  chain 
of  ordinary  generation  is  once  broken.  Tlie  gradual  diffusion 
of  dominant  forms,  with  the  slow  modification  of  their  descend- 
ants, causes  the  forms  of  life,  after  long  intervals  of  time,  to 
appear  as  if  they  had  changed  simultaneously  throughout  the 
world.  The  fact  of  the  fossil  remains  of  each  formation  being 
in  some  degree  intermediate  in  character  between  the  fossils 
in  the  formations  above  and  below,  is  simpl}'  ex])lained  by 
their  intermediate  position  in  the  chain  of  descent.  The  grand 
fact  that  all  extinct  beings  can  be  classed  with  all  recent 
beings,  naturally  follows  from  the  liWng  and  the  extinct  being 
the  ofispring  of  common  parents.  As  species  have  generally 
diverged  in  character  during  their  long  course  of  descent  and 
modiiication,  we  can  understand  why  it  is  that  the  more  an- 
cient forms  of  early  progenitors  of  each  group  so  often  occu- 
py a  position  in  some  degree  intermediate  between  existing 
groups.  Recent  forms  are  generally  looked  at  as  being,  on 
the  whole,  higher  in  the  scale  of  organization  than  ancient 
forms ;  and  they  must  bo  higher,  in  so  far  as  the  later  and 
more  improved  forms  have  conqu(>red  the  older  and  less  im- 
proved forms  in  the  struggle  of  life;  they  have  also  generally 
had  their  organs  more  spccializtnl  for  different  functions.  This 
fact  is  ])('rfectly  cfjmpatible  with  numerous  beings  still  retain- 
ing simpl(!  and  but  little  improved  structures,  iitled  for  simple 
condilicjns  of  life  ;  it  is  likewise  compatible  with  some  forms 
haWng  retrograded  in  organization,  by  having  become  at  each 
stage  of  descent  better  fitted  for  changed  and  degraded  habits 


420  BECAPITULATION.  •  Chap.  XIV. 

of  life.  Lastly,  the  wonderful  law  of  the  long  endurance  of 
allied  forms  on  the  same  continent — of  marsupials  in  Australia, 
of  edenlatii  in  America,  anct  other  such  cases — is  intelligible, 
for  generally  within  the  same  country  the  existing  and  the  ex- 
tinct will  be;  closely  allied  l)y  descent. 

Looking  to  geographical  distribution,  if  wc  admit  that 
there  has  been  during  the  long  course  of  ages  much  migration 
from  one  part  of  the  world  to  another,  owing  to  former  clima- 
tal  and  geographical  changes  and  to  the  many  occasional  and 
unknown  means  of  dispersal,  then  wc  can  understand,  on  the 
theory  of  descent  with  modification,  most  of  the  great  leading 
facts  in  Distribution.  We  can  see  why  there  should  be  so 
striking  a  parallelism  in  the  distribution  of  organic  beings 
throughout  space,  and  in  their  geological  succession  through- 
out time  ;  for  in  both  cases  the  beings  have  been  connected  by 
the  bond  of  ordinary  generation,  and  the  means  of  modifica- 
tion have  been  the  same.  We  see  the  full  meaning  of  the 
wonderful  fact,  which  has  struck  every  traveller,  namely,  that 
on  the  same  continent,  under  the  most  diverse  conditions, 
luider  heat  and  cold,  on  mountain  and  lowland,  on  deserts  and 
marshes,  most  of  the  inhabitants  within  each  great  class  are 
plainly  related ;  for  they  are  the  descendants  of  the  same  pro- 
genitors and  early  colonists.  On  this  same  principle  of  former 
migration,  combined  in  most  cases  with  modification,  we  can 
unclerstand,  by  the  aid  of  the  Glacial  period,  the  identity  of 
some  few  plants,  and  the  close  alliance  of  many  others,  on  the 
most  distant  mountains,  and  in  the  northern  and  southern  tem- 
perate zones ;  and  likewise  the  close  alliance  of  some  of  the 
inhabitants  of  the  sea  in  the  northern  and  southern  temperate 
latitudes,  though  separated  by  the  whole  intertropical  ocean. 
Although  two  countries  may  present  physical  conditions  as 
closely  similar  as  the  same  species  ever  reqviire,  we  need  feel 
no  surprise  at  their  inhabitants  being  widely  different,  if  they 
have  been  for  a  long  period  completely  sundered  from  each 
other ;  for,  as  the  relation  of  organisn\  to  organism  is  the  most 
important  of  all  relations,  and  as  the  two  countries  will  have 
received  colonists  at  various  periods  and  in  difi'erent  propor- 
tions, from  some  other  country  or  from  each  other,  the  course 
of  modification  in  the  two  areas  will  ineWtably  have  been  dif- 
ferent. 

On  this  view  of  migration,  with  subsequent  modification, 
we  see  why  oceanic  islands  arc  inhabited  by  only  few  species, 
but  of  these,  why  many  arc  peculiar  or  endemic  forms.     We 


CiiAi-.  XIV  EECAPITULATION.  497 

clearly  sec  why  species  belonging  to  those  groups  of  animals 
which  cannot  cross  wide  spaces  of  the  ocean,  as  frogs  and  ter- 
restrial niumnials,  do  not  inhabit  oceanic  islands  ;  and  wliy,  on 
the'  other  hand,  new  and  peculiar  species  of  bats,,  animals 
wliich  can  traverse  the  ocean,  are  so  often  found  on  islands  far 
distant  from  any  contni(?nt.  Such  cases  as  the  presence  of  pe- 
culiar species  of  bats  on  oceanic  islands,  and  the  absence  of 
all  other  terrestrial  mammals,  are  facts  utterly  inexplicable  on 
the  theory  of  independent  acts  of  creation. 

The  existence  of  closely-allied  or  representative  species  in 
any  two  areas,  implies,  on  the  theory  of  descent  with  modifica- 
tion, that  the  same  parent-forms  formerly '  inhabited  both 
areas ;  and  we  almost  invariably  find  that,  wherever  many 
closely-allied  species  inhabit  two  areas,  some  identical  species 
are  still  conunon  to  both.  Wherever  many  closely-allied  yet 
distinct  species  occur,  doubtful  forms  and  varieties  belonging 
to  the  same  groups  likewise  occur.  It  is  a  rule  of  high  gener- 
ality that  the  inhabitants  of  each  area  are  related  to  the  inhabi- 
tants of  the  nearest  source  whence  innnigrants  might  have 
been  derived.  We  see  this  in  the  striking  relation  uf  nearly 
all  the  plants  and  animals  of  the  Galapagos  archipelago,  of 
Juan  Fernandez,  and  of  the  other  American  islands,  to  the 
plants  and  animals  of  the  neighboring  American  main-land  ;  and 
of  those  of  the  Cape  de  Verde  archipelago  and  of  the  other 
African  islands  to  the  African  main-land.  It  must  be  admitted 
that  these  facts  receive  no  explanation  on  the  theory  of  crea- 
tion. 

The  fact,  as  we  have  seen,  that  all  past  and  present  organ- 
ic beings  can  be  arranged  within  a  few  great  classes,  in  groups 
subordinate  to  groups,  and  with  the  extinct  groups  often  fall- 
ing in  between  the  recent  groups,  is  intelligible  on  the  tlieory 
of  natural  selection  with  its  contingencies  of  extinction  and 
divergence  of  character.  On  these  same  princijilcs  we  see  how 
it  is  that  the  mutual  affinities  of  the  forms  Avithin  each  class 
are  so  complex  and  circuitous.  We  see  why  cert^iin  charac- 
ters are  far  more  seniceable  than  others  fur  classification — 
why  adaptive  characters,  though  of  paramount  imjiortance  to 
the  beings,  are  of  hardly  any  importance  in  classification  ; 
why  characters  derived  from  rudimentary  parts,  though  of  no 
service  to  the  beings,  are  often  of  high  classiiicatory  value; 
and  why  embryological  charactei-s  are  often  the  most  valuable 
of  all.  The  real  affinities  of  all  organic  beings,  in  contradis- 
tinction to  tiieir  adaptive  resemblances,  are  due  to  inheritance 


428  EECAPITDLATION,  Chap.  X[V. 

or  coinimniity  of  descent.  The  Natural  System  is  a  genealo- 
gical arrangement,  with  the  acquired  grades  of  difference, 
marked  by  tlic  terms,  varieties,  species,  genera,  families,  etc. ; 
and  we  kavc  to  discover  the  lines  of  descent  by  the  most  per- 
manent characters,  whatever  they  may  be  and  of  however  slight 
vital  importance. 

The  singular  framework  of  bones  in  the  hand  of  a  man, 
wing  of  a  bat,  fin  of  the  porpoise,  and  leg  of  the  horse — the  same 
ninuber  of  vertebras  forming  the  neck  of  the  giraffe  and  of  the 
elephant — and  innumerable  other  such  facts,  at  once  explain 
themselves  on  the  theory  of  descent  with  slow  and  slight  suc- 
cessive modifications.  Tlic  similarity  of  pattern  in  the  w'ing 
and  in  the  leg  of  a  bat,  though  used  for  such  different  purpose 
— in  the  jaws  and  legs  of  a  crab^in  the  petals,  stamens,  and 
pistils  of  a  flower — is  likewise  intelligible  on  the  view  of  the 
gradual  modification  of  parts  or  organs,  which  were  aborigi- 
nally alike  in  an  early  progenitor  in  each  of  these  classes.  On 
the  principle  of  successive  variations  not  always  supervening  at 
an  early  age,  and  being  inherited  at  a  corresponding  not  early 
period  of  life,  we  clearly  see  why  the  embryos  of  mammals, 
birds,  reptiles,  and  fishes,  are  so  closely  similar,  and  so  unlike 
the  adult  forms.  We  may  cease  marvelling  at  the  embryo  of 
an  air-breathing  mammal  or  bird  having  branchial  slits  and 
arteries  running  in  loops,  like  those  of  a  fish  which  has  to 
breathe  air  dissolved  in  water  by  the  aid  of  well-developed 
branchiiv. 

Disuse,  aided  sometimes  by  natural  selection,  has  often 
reduced  organs  when  they  have  become  useless  under  changed 
halnts  or  conditions  of  life  ;  and  we  can  clearly  understand  on 
this  vfew  the  meaning  of  rudimentary  organs.  But  disuse  and 
selection  will  generally  act  on  each  creature,  when  it  has  come 
to  maturity  and  has  to  play  its  full  part  in  the  struggle  for  ex- 
istence, and  Avill  thus  have  little  power  on  an  organ  during 
early  life ;  hence  the  organ  will  not  be  reduced  or  rendered 
rudimentary  at  this  early  age.  The  calf,  for  instance,  has  in- 
herited teeth,  which  never  cut  through  the  gums  of  tlie  upper 
jaw,  from  an  early  progenitor  having  well-developed  teeth  ; 
and  we  may  believe,  that  the  teeth  in  the  mature  animal  were 
reduced,  during  successive  generations,  by  disuse,  or  by  the 
tongue  and  palate,  or  lips,  ha^^ng  become  better  fitted  by 
natural  selection  to  browse  without  their  aid  ;  whereas  in  the 
calf,  tlie  teeth  have  been  left  imtouched  by  selection  or  disuse, 
and  on  the  principle  of  inheritance  at  corresponding  ages  have 


CuAP.  XIV.  CONCLUSION.  429 

been  inherited  from  a  remote  period  to  llie  present  day.  On 
the  view  of  each  organic  being  with  all  its  separate  parts  hav- 
ing been  specially  created,  how  utterly  inexplicable  it  is  that 
(Mgans  bearing  the  plain  stamp  of  inutility,  such  as  the  teeth  in 
the  embryonic  calf  or  the  shrivelled  wings  under  the  soldered 
\ving-covers  of  many  beetles,  should  so  frequently  occur  !  Na- 
ture may  be  said  to  have  taken  pains  to  reveal  her  schejne  of 
modification,  by  means  of  rudimentary  organs,  embryological 
and  homologous  structures,  but  we  wilfully  will  not  understand 
the  scheme. 

I  have  now  recapitulated  the  facts  and  considerations 
which  have  thoroughly  convinced  me  that  species  have  been 
modiiied,  (hiring  a  long  course  of  descent,  chiefly  through  the 
natural  selection  of  numerous  successive,  slight,  favorable  va- 
riations. I  cannot  believe  that  a  false  theory  would  explain, 
as  it  seems  to  me  that  the  theory  of  natural  selection  does  ex- 
plain, the  several  large  classes  of  facts  above  specified.  It  is 
no  valid  objection  that  science  as  yet  throws  no  light  on  the 
far  higher  problem  of  the  essence  or  origin  of  life.  A\'ho  can 
explain  what  is  the  essence  of  the  attraction  of  gravity  ?  No 
()n<;  now  objects  to  following  out  the  results  consequent  on 
this  xmknown  element  of  attraction;  notwithstanding  that 
Leibnitz  formerly  accused  Newton  of  introducing  "occult 
qualities  and  miracles  into  philosophy." 

I  see  no  good  reason  Avhy  the  views  given  in  this  volume 
should  shock  the  religious  feelings  of  any  one.  It  is  satisfac- 
tory, as  showing  how  transient  such  impressions  are,  to  remem- 
Ixn-  thiit  the  greatest  discovery  ever  made  by  man,  namely,  the 
law  of  the  attraction  of  gravity,  was  also  attacked  by  Leibnitz, 
"  as  subversive  of  natural  and  inferentially  of  revealed  reli- 
gion." A  celebrated  author  and  divine  has  written  to  me  that 
"  he  has  gradually  learned  to  see  that  it  is  just  as  noble  a  con- 
eej^tion  of  the  Deity  to  believe  that  lie  created  a  few  original 
forms  capable  of  self-development  into  other  and  needful 
forms,  as  to  believe  that  He  recpiired  a  fresh  act  of  creation  to 
suj)])ly  the  voids  caused  by  the  action  of  His  laws." 

Why,  it  may  be  asked,  imtil  recently  did  nearly  all  the 
most  eminent  living  naturalists  and  geologists  reject  this  view 
of  tin;  mutability  of  species.  It  cannot  be  asserted  that 
organic  b(Mngs  in  a  state  of  nature  are  subject  to  no  variation; 
it  caimot  be  jiroved  that  the  amount  of  variation  in  the  course 
of  long  ages  is  a  limited  quantity ;  no  clear  distinction  has 


430  CONCLUSION.  Chap.  XIV. 

been,  or  cjin  bo,  (hawn  between  species  and  well-marked  varie- 
ties. It  cannot  be  maintained  that  species  when  intercrossed 
are  invariably  sterile,  and  varieties  invariably  fertile ;  or  that 
sterility  is  a  special  endowment  and  sign  of  creation.  The  be- 
lief tliat  species  were  immutable  productions  was  almost  una- 
voidable ;is  lon;!^  as  the  history  of  the  world  was  thought  to  be 
of  shoct  duration  ;  and  now  that  we  have  acquired  some  idea 
of  the  lapse  of  time,  Ave  are  too  apt  to  assume,  without  proof, 
that  the  geological  record  is  so  perfect  that  it  would  have 
alforded  us  plain  evidence  of  the  mutation  of  species,  if  they 
had  undergone  nmtation. 

But  the  chief  cause  of  oin-  natural  unwillingness  to  admit 
that  one  species  has  given  birth  to  other  and  distinct  species, 
is,  that  we  are  always  slow  in  admitting  any  great  change  of 
which  we  do  not  see  the  steps.  The  difficulty  is  the  same  as 
that  felt  by  so  many  geologists,  Avhen  Lyell  first  insisted  that 
long  lines  of  inland  cliffs  had  been  formed,  and  great  valleys 
excavated,  by  the  agencies  Avhich  we  see  still  at  Avork.  The 
mind  cannot  possibly  grasp  the  full  meaning  of  the  term  of 
even  ten  million  years ;  it  cannot  add  up  and  perceive  the  full 
effects  of  many  slight  A'ariations,  accumulated  during  an  almost 
hillnite  number  of  generations. 

Although  I  am  fully  convinced  of  the  truth  of  the  A'ieAVS 
giA'en  in  this  Aolume  under  the  fonn  of  an  abstract,  I  by  no 
means  expect  to  convince  experienced  naturalists  Avhose  minds 
are  stocked  Avitli  a  multitude  of  facts  all  A'iewed,  during  a  long 
course  of  years,  from  a  point  of  vicAV  directly  opposite  to  mine. 
It  is  so  easy  to  hide  our  ignorance  under  such  expressions  as 
the  "  plan  of  creation,"  "  unity  of  design,"  etc.,  and  to  think 
that  Ave  giA'e  an  ex2:)lanation  Avhen  Ave  only  restate  a  fact  ! 
Any  one  Avhose  disposition  leads  him  to  attach  more  Aveight 
to  unexjilained  difficulties  than  to  the  explanation  of  a  certain 
numl)er  of  facts,  Avill  certainly  reject  the  theory.  A  fcAV  natu- 
ralists, endoAA'ed  Avith  much  flexibility  of  mind,  and  Avho  liaA'e 
already  begun  to  doubt  the  immutability  of  species,  may  be 
induouced  by  this  volume ;  but  I  look  Avith  confidence  to  the 
future,  to  young  and  rising  naturalists,  Avho  Avill  be  able  to 
view  both  sides  of  the  question  Avith  impartiality,  ^^'hoeve^ 
is  led  to  bclicA'e  that  species  are  mutable  Avill  do  good  service 
by  conscientiously  expressing  his  conA'iction  ;  for  thus  only 
can  tlie  load  of  prejudice  by  Avhich  this  subject  is  overwhelmed 
be  removed. 

Several  eminent  naturalists  have  of  late  published    tluir 


Chap.  XIV.  CONCLUSION.  431 

belief  that  a  multitude  of  reputed  species  in  each  genus  arc 
not  real  species ;  but  tliat  othor  species  are  real,  that  is,  have 
been  independently  created.  This  seems  to  me  a  strange  con-- 
elusion  to  arrive  at.  They  admit  tliat  a  multitude  of  forms, 
which  till  lately  they  themselves  thought  were  special  crea- 
tions, and  which  arc  still  thus  looked  at  by  the  majority  of 
naturalists,  and  which  consequently  have  all  the  external  char- 
acteristic features  of  true  species — they  admit  that  these  have 
been  produced  by  variation,  but  they  refuse  to  extend  the 
same  view  to  other  and  slightly-different  forms.  Nevertheless 
they  do  not  pretend  that  they  can  defuie,  or  even  conjecture, 
which  are  the  created  forms  of  life,  and  which  arc  those  pro- 
duced by  secondary  laws.  They  admit  variation  as  a  vera 
causa  in  one  case,  they  arbitrarily  reject  it  in  another,  without 
assigning  any  distinction  in  the  two  cases.  The  day  will  come 
when  this  will  be  given  as  a  curious  illustration  of  the  blind- 
ness of  preconceived  opinion.  These  authors  seem  no  more 
startled  at  a  miraculous  act  of  creation  than  at  an  ordinary 
birth.  But  do  they  really  believe  that  at  innumerable  periods 
in  the  earth's  history  certain  elemental  atoms  have  been  com- 
manded suddenl}'  to  flash  into  living  tissues  ?  Do  they  believe 
that  at  each  supposed  act  of  creation  one  individual  or  many 
were  jiroduced  ?  Were  all  the  infinitely-numerous  kinds  of 
animals  and  plants  created  as  eggs  or  seed,  or  as  full  grown  ? 
and,  in  the  case  of  mammals,  were  they  created  bearing  the 
false  marks  of  nourishment  fron^  the  mother's  womb  ?  Un- 
doubtedly these  same  questions  cannot  be  answered  by  those 
who  believe  in  the  appearance  or  creation  of  only  a  few  forms 
of  life,  or  of  some  one  form  alone.  It  has  been  maintained  by 
several  authors  that  it  is  as  easy  to  believe  in  the  creation  of 
a  hundred  million  beings  as  of  one ;  but  Maupertuis's  philo- 
sophical axiom  "  of  least  action"  leads  the  mind  more  willing- 
ly to  admit  the  smaller  number  ;  and  certainly  we  ought  not 
to  believe  that  innumerable  l)eings  within  each  great  class 
have  been  created  with  plain,  but  deceptive,  marks  of  descent 
from  a  single  parent. 

It  may  be  asked  how  far  I  extend  the  doctrine  of  the  mod- 
ification of  species.  The  question  is  diiricult  to  answer,  be- 
cause the  more  distinct  the  forms  are  which  we  consider,  by  so 
much  the  arguments  fall  away  in  force.  But  some  arguments 
of  the  greatest  weight  extend  very  far.  All  the  memliers  of 
whole  classes  are  connected  together  by  a  chain  of  affinities, 
and  all  can  be  classified  on  the  same  principle,  in  groups  subor- 


432  CONCLUSION.  Chap.  XIV. 

dinatc  to  groups.  Fossil  remains  sometimes  tend  to  fill  up 
very  wide  intervals  between  existing  orders.  Organs  in  a  rudi- 
mentary condition  plainly  show  that  an  early  progenitor  had 
the  organ  in  a  fully-developed  state  ;  and  this  in  some  instances 
implies  an  enormous  amount  of  modification  in  the  descend- 
ants. Tlnoughoiit  whole  classes  various  structures  are  formed 
on  the  same  ])attcrn,  and  at  a  very  early  age  the  embryos 
closely  resemble  each  other.  Therefore  I  cannot  doubt  that 
tlie  theory  of  descent  with  modification  embraces  all  the  mem- 
bers of  the  same  class.  I  believe  that  animals  are  descended 
from  at  most  only  four  or  five  progenitors,  and  plants  from  an 
equal  or  lesser  number. 

Analogy  would  lead  me  one  step  further,  namely,  to  the 
belief  that  all  animals  and  plants  are  descended  from  some  one 
prototype.  But  analogy  may  be  a  deceitful  guide.  Neverthe- 
less all  living  things  have  much  in  common — in  their  chemical 
composition,  their  cellular  structure,  their  laws  of  growth,  and 
their  liability  to  injurious  influences.  We  see  this  even  in  so 
trifling  a  fact  as  that  the  same  poison  often  similarly  affects 
plants  and  animals  ;  or  that  the  poison  secreted  by  the  gall-fly 
produces  monstrous  growths  on  the  wild  rose  or  oak-tree. 
^Vith  all  organic  beings  sexual  reproduction  seems  to  be  essen- 
tially similar.  With  all,  as  far  as  is  at  present  known,  the 
germinal  vesicle  is  the  same ;  so  that  all  organisms  start  from 
a  common  origin.  If  we  look  even  to  the  two  main  divisions 
— namely,  to  tlie  animal  and  vegetable  kingdoms — certain  low 
forms  arc  so  fiir  intermediate  in  character  that  naturalists  have 
disputed  to  which  kingdom  they  should  be  referred,  and,  as 
Prof.  Asa  Gray  has  remarked,  "  tlie  spores  and  other  reproduc- 
tive bodies  of  many  of  the  lower  alga3  may  claim  to  have  first 
a  characteristically  animal,  and  then  an  unequivocally  vegetable 
existence."  Therefore,  on  the  principle  of  natural  selection 
with  divergence  of  character,  it  does  not  seem  incredible  that, 
from  some  such  low  and  intermediate  form,  both  animals  and 
plants  may  have  been  developed ;  and,  if  we  admit  this,  we 
must  likewise  admit  that  all  the  organic  beings  Avhich  have 
ever  lived  on  this  earth  may  be  descended  from  some  one  pri- 
mordial form.  But  this  infei'ence  is  chiefly  grounded  on  anal- 
ogy, and  it  is  immaterial  whether  or  not  it  be  accepted.  No 
doubt  it  is  possible,  as  Mr.  G.  H.  Lewes  has  urged,  that  at  the 
first  commencement  of  life  many  difl'erent  forms  were  evolved; 
but  if  so,  we  may  conclude  that  only  a  very  few  have  left  modi- 
fied descendants.    For,  as  I  have  recently  remarked  in  regard  to 


CflAP.  XIV.  CONCLUSION.  433 

the  members  of  each  great  class,  such  as  the  Vertebrata,  Artio- 
ulataj  etc.,  Ave  have  distinct  evidence  in  their  embryological, 
homologous,  and  rudimentary  structures,  that  within  each  class 
all  are  descended  from  a  single  progenitor. 

When  the  views  advanced  by  me  in  this  volume,  and  by 
Mr.  Wallace  in  the  Linncan  Journal,  or  when  analogous  views 
on  the  origin  of  species  are  generally  admitted,  Ave  can  dimly 
foresee  that  there  will  be  a  considerable  revolution  in  natural 
liistory.  Systematists  will  be  able  to  pursue  their  labors  as  at 
present ;  but  they  Avill  not  be  incessantly  haunted  by  the  shad- 
owy doubt  whether  this  or  that  form  be  a  true  species.  This 
I  feel  sure,  and  I  speak  after  experience,  will  be  no  slight  re- 
lief. The  endless  disputes  whether  or  not  some  fifty  species 
of  British  brambles  are  good  species  will  cease.  Systematists 
will  have  only  to  decide  (not  that  this  will  be  easy)  whether 
any  form  be  sufficiently  constant  and  distinct  from  other  forms, 
to  be  capable  of  definition ;  and  if  definable,  whether  the  dif- 
ferences be  sufficiently  important  to  deserve  a  specific  name. 
Tliis  latter  point  Avill  become  a  far  more  essential  consideration 
than  it  is  at  present ;  for  differences,  however  slight,  between 
any  two  forms,  if  not  blended  by  intermediate  gradations,  are 
looked  at  by  most  naturalists  as  sufficient  to  raise  both  forms 
to  the  rank  of  species.  Hereafter  Ave  shall  be  compelled  to 
acknoAvledgc  that  the  only  distinction  Ijctween  species  and 
Avell-maiked  varieties  is,  that  the  latter  arc  knoAvn,  or  believed, 
to  be  connected  at  the  ]iresent  day  by  intermediates  gradations, 
whereas  species  Avere  formerly  thus  connected.  Hence,  Avith- 
out  rejecting  the  consideration  of  the  present  existence  of  in- 
Icnnediate  gradations  between  any  two  forms,  Ave  shall  be  led 
to  Avelgh  more  carefully  and  to  A'alue  higher  the  actual  amount 
of  dillcrence  between  them.  It  is  quite  jiossible  that  forais  noAV 
generally  acknowledged  to  be  merely  varieties  may  hereafter 
l)o  thought  Avorthy  of  specific  names ;  and  in  this  case  scien- 
tific and  common  language  Avill  come  into  accordance.  In 
short,  Ave  shall  liaA'C  to  treat  species  in  the  same  manner  as 
those  naturalists  treat  genera,  Avho  admit  that  genera  are 
merely  artificial  combinations  made  for  conA'cnience.  Tliis 
may  not  be  a  cheering  prospect;  but  avc  shall  at  least  be  freed 
from  the  A'ain  search  for  the  undiscovered  and  undiscoverable 
essence  of  the  term  sj)ecies. 

The  other  and  more  general  departments  of  natural  history 
Avill  rise  greatly  in  interest.  The  terms  used  l>y  naturalists  of 
allinitv,  relationship,  community  of  type,  paternitv,  morpholo- 
10 


434  CONCLUSION.  Cbap.  XIV 

gy,*  adaptive  cliaraclcrs,  rudimeiitaiy  and  abortive  organs,  etc., 
Avill  cease  to  be  nietaphorica],  and  will  have  a  plain  significa- 
tion. AVhen  we  no  longer  look  at  an  organic  being  as  a  sav- 
age looks  at  a  ship,  as  something  wholly  beyond  his  compre- 
hension ;  when  we  regard  every  production  of  Nature  as  one 
which  has  had  a  long  history ;  when  we  contemplate  every  com- 
plex structure  and  instinct  as  the  summing  up  of  many  con- 
trivances, each  useful  to  the  possessor,  in  the  same  way  as  any 
great  mechanical  invention  is  the  summing  up  of  the  labor, 
the  experience,  the  reason,  and  even  the  blunders  of  numerous 
workmen ;  when  we  thus  view  each  organic  being,  how  far 
more  interesting — I  speak  from  experience — does  the  study 
of  natural  history  become  ! 

A  grand  and  almost  untrodden  field  of  inquiry  will  be 
opened,  on  tlie  causes  and  laws  of  variation,  on  correlation,  on 
•the  effects  of  use  and  disuse,  on  the  direct  action  of  external 
conditions,  and  so  forth.  The  study  of  domestic  productions 
will  rise  immensely  in  value.  A  new  variety  raised  by  man 
will  be  a  more  important  and  interesting  subject  for  study 
than  one  more  sjiecies  added  to  the  infinitude  of  already-re- 
corded species.  Our  classifications  will  come  to  be,  as  far  as 
they  can  be  so  made,  genealogies ;  and  Avill  then  truly  give 
what  may  be  called  the  plan  of  creation.  The  rules  for  classi- 
fying will  no  doubt  become  simpler  when  we  have  a  definite 
object  in  view.  We  possess  no  pedigrees  or  armorial  bear- 
ings ;  and  we  have  to  discov' cr  and  trace  the  many  diverging 
lines  of  descent  in  our  natural  genealogies,  by  characters  of 
any  kind  wliich  have  long  been  inherited.  Rudimentary  or- 
gans will  speak  infallibly  with  respect  to  the  nature  of  long- 
lost  structures.  Species  and  groups  of  species,  which  are 
called  aberrant,  and  wliich  may  fancifully  be  called  living  fos- 
sils, will  aid  us  in  forming  a  picture  of  the  ancient  forms  of 
life.  Embryology  will  often  reveal  to  us  the  structure,  in 
some  degree  obscured,  of  the  prototypes  of  each  great  class. 

A\'lien  we  can  feel  assured  that  all  the  individuals  of  the 
same  species,  and  all  the  closely-allied  species  of  most  genera, 
have  within  a  not  very  remote  period  descended  from  one 
parent,  and  have  migrated  from  some  one  birthplace;  and 
Avhen  we  better  know  the  many  means  of  migration,  then,  by 
the  light  which  geology  now  throws,  and  will  continue  to 
throw,  on  former  changes  of  climate  and  of  the  level  of  the 
land,  we  shall  surely  be  enabled  to  trace  in  an  admirable  man- 
ner   the    former  migrations  of  the  inhabitants   of  the  whole 


Chat.  XIV.  CONCLUSION.  •  435 

world.  Even  at  present,  by  comparing  the  differences  of  the 
inluibitaiits  of  tlie  sea  on  the  opposite  sides  of  a  continent, 
and  the  nature  of  the  various  inhabitants  of  that  continent  in 
relation  to  tlicir  apparent  means  of  immig-ration,  some  light 
can  be  thrown  on  ancient  geography. 

The  noble  science  of  Geology  loses  glory  from  the  ex- 
treme imperfection  of  the  record.  The  crust  of  the  earth  Avith 
its  embetlded  remains  must  not  be  looked  at  as  a  well-filled 
museum,  but  as  a  poor  collection  made  at  hazard  and  at  rare 
intervals.  The  accumulation  of  each  great  fossiliferous  forma- 
tion will  be  recognized  as  having  depended  on  an  nnusual  con- 
currence of  favorable  circumstances,  and  the  l)lank  intervals 
between  the  successive  stages  as  having  been  of  vast  duration. 
But  we  shall  be  able  to  gauge  with  some  security  the  duration 
of  these  intervals  by  a  comparison  of  the  preceding  and  suc- 
ceeding organic  forms.  We  must  be  cautious  in  attempting  to 
correlate  as  strictly  contemporaneous  two  formations,  wliicli  do 
not  include  many  identical  species,  by  the  general  succession 
of  the  forms  of  life.  As  species  are  produced  and  extermi- 
nated by  slowly  acting  and  still  existing  causes,  and  not  hy  mi- 
raculous acts  of  creation  and  by  catastrophes ;  and  as  the  most 
important  of  all  causes  of  organic  change  is  one  which  is  al- 
most independent  of  altered  and  perliaps  suddenly-altered 
])hysical  conditions,  namely,  the  mutual  relation  of  organism  to 
organism — the  improvement  of  one  organism  entailing  the  im- 
provement or  the  extermination  of  others — it  follows  that  the 
amount  of  organic  change  in  the  fossils  of  consecutive  forma- 
tions probably  serves  as  a  fair  measure  of  the  lapse  of  actual 
time.  A  number  of  species,  however,  keeping  in  a  body 
might  remain  for  a  long  period  unchanged,  while  within  this 
same  period,  sevend  of  these  species,  by  migrating  into  new 
countries  and  coming  into  competition  with  foreign  associates, 
might  become  modilied  ;  so  that  we  nmst  not  overrate  the  ac- 
curacy of  organic  change  as  a  measure  of  time.  During  earlv 
periods  of  the  earth's  liistory,  when  the  forms  of  life  were  proba- 
i)ly  fewer  and  simpler,  the  rate  of  change  was  ])rol)ably  slower; 
and  at  the  fust  dawn  of  life,  when  very  few  forms  of  the  sim- 
plest structure  existed,  the  rate  of  change  niav  have  been  slow 
in  an  extreme  degree.  The  history  of  tlie  wt)rld,  as  at  present 
known,  although  of  innnense  length,  will  liereaiter  be  reco""- 
nized  as  short,  compared  with  the  ages  which  must  have 
eUipsed  since  the  first  organic  beings,  the  progenitors  of  in- 
numerable extinct  and  living  descendants,  appeared  on  the 
stay-e. 


436  •  CONCLUSIOxV.  Cuap.  XIV. 

In  the  distant  future  I  see  open  fields  for  far  more  impor- 
tant researclics.  Psychology  Avill  be  based  on  a  new  founda- 
tion, that  of  the  necessary  acquirement  of  each  mental  power 
and  capacity  by  gradation.  Light  Avill  be  thrown  on  the  origin 
of  man  and  his  history. 

Authors  of  the  highest  eminence  seem  to  be  fully  satisfied 
with  the  view  that  each  species  has  been  independently  cre- 
ated. To  my  mind  it  accords  better  with  what  avc  know  of 
the  laws  impressed  on  matter  by  the  Creator,  that  the  pro- 
duction and  extinction  of  the  past  and  present  inhabitants  of 
the  world  should  have  been  due  to  secondary  causes,  like 
those  determining  the  birth  and  death  of  the  individual. 
"When  I  Adew  all  beings  not  as  special  creations,  but  as  the 
lineal  descendants  of  some  few  beings  which  lived  long  be- 
f<.)rc  the  first  bed  of  the  Silurian  system  was  deposited,  tliey 
seem  to  me  to  become  ennobled.  Judging  from  the  past,  we 
may  safely  infer  that  not  one  living  species  will  transmit  its 
imaltcred  likeness  to  a  distant  futurit}'.  And  of  the  species 
now  living  very  few  will  transmit  progeny  of  any  kind  to  a 
far-distant  futurity ;  for  the  manner  in  which  all  organic  be- 
ings are  grouped,  shows  that  the  greater  number  of  species  in 
each  genus,  and  all  the  species  in  many  genera,  have  left  no 
descendants,  but  have  become  utterly  extinct.  We  can  so  far 
take  a  prophetic  glance  into  futurity  as  to  foretell  that  it  will  be 
the  connnon  and  widely-spread  species,  belonging  to  the  larger 
and.<l<)minant  groups  within  each  class, nvhich  will  ultimately 
prevail  and  procreate  new  and  dominant  species.  As  all  the 
living  forms  of  life  are  the  lineal  descendants  of  those  which 
lived  long  before  the  Silurian  epoch,  we  may  feel  certain  that 
the  ordinary  succession  by  generation  has  never  once  been 
broken,  and  that  no  cataclysm  has  desolated  the  whole  world. 
Hence  we  may  look  with  some  confidence  to  a  secure  future 
of  equally  inappreciable  length.  And  as  natural  selection 
works  solely  by  and  for  the  good  of  each  being,  all  corporeal 
and  mental  endowments  will  tend  to  progress  toward  perfec- 
tion. 

It  is  interesting  to  contemplate  a  tangled  bank,  clothed 
with  many  plants  of  many  kinds,  with  birds  singing  on  the 
bushes,  witli  various  insects  Hitting  about,  and  Avith  Avorms 
crawling  through  the  damp  earth,  and  to  reflect  that  these  elab- 
orately constructed  forms,  so  dift'erent  from  each  other,  and 
dependent  on  each  other  in  so  complex  a  manner,  have  all  been 
produced  by  laAvs  acting  around  us.     Tliesc  laws,  taken  in  the 


Cir.u-.  XIV.  CONCLUSION.  437 

largest  sense,  being  Growth  with  Reproduction ;  Inheritance 
which  is  ahnost  inipUed  by  reproduction  ;  Variahility  from  the 
inchrcct  and  direct  action  of  the  conditions  of  Ufe,  and  from 
use  and  disuse  ;  a  Katio  of  Increase  so  high  as  to  lead  to  a 
Struggle  for  Life,  and  as  a  consequence  to  Natural  Selection, 
entailing  Divergence  of  Character  and  the  Extinction  of  less- 
improved  forms.  Thus,  from  the  war  of  Nature,  from  famine 
and  death,  the  most  exalted  object  Avhich  we  are  capable  of 
conceiving,  namely,  the  production  of  the  higher  animals,  di- 
rectly follows.  There  is  grandeur  in  this  view  of  life,  with  its 
several  powers,  having  been  originally  breathed  by  the  Crea- 
tor into  a  few  forms  or  into  one ;  and  that,  while  this  planet 
has  gone  cycling  on  according  to  the  fixed  law  of  gravity,  from 
so  simple  a  beginning  endless  forms  most  beautiful  and  most 
wonderful  have  been,  and  are  being,  evolved. 


INDEX 


Aberrant  groups,  387. 

AbvKsinin,  plants  of,  3-18. 

Acclimatization,  111. 

Atloxa,  12i). 

Affinities  of  extinct  species,  307. 

of  organic  beings,  3S6. 
Agassiz,  on  Amblj'opsis,  113. 

on  groups  of  species  suddenly  ap- 
peiiriiiLT,  2'M. 

on  enibry<il()L'ical  succession,  316. 

on  the  (ilaci;il  period,  837. 

ou  cnibrvological  characters,  378. 

on  the  lalep't  tertiary  forms,  2S2. 

ou  parallelism  of  embryological  de- 
velopment and  geological  bucccs- 
sion,  534. 
AIotj  of  Kew  Zealand.  3-1.5. 
Alligators,  males.  fii:li!iii'_',  91. 
Alternate  ji^eneralions,  '.','.)[. 
Amblyopsis.  blind  lish,  1 13. 
America,  North,   productions   allied    to 
tliose  of  Europe,  340. 

North,  bowlders  and  glaciers  of,  .343. 

South,  no  modern  formations  ou  west 
coast,  275. 
Ammcmites,  sudden  extinction  of,  .302. 
Anagallis,  sterility  of,  235. 
Analogy  of  variations,  100. 
Ancylus,  a")3. 
Andaman  Islands  inhabited  by  a  toad, 

aj8. 
Animals,  not  domesticated    from  being 

variable,  30. 
Animals,  domestic,  descended  from  sev- 
eral stocks,  .32. 

domestic,  acclimatization  of,  11-4. 

of  Australia,  113. 

with  thicker  fur  in  cold  climates,  133. 

blind,  in  caves.  111. 

extinct,  of  Australia,  310. 
Anoinma,  229. 

Antarctic  islands,  ancient  flora  of,  303. 
Ants  atlondiiiL:  aphides,  201. 

sluve-TiKikiiii:  instinct.  212. 

neuter,  strnctiire  of,  22ti. 
Aidiides,  attended  by  ants,  203. 
Aphis,  development'of,  898. 
Apteryx,  170. 
Anil)  horses,  41. 
Arulo-C'aspian  Sea,  317. 


Archeopteryx,  288. 

Archiac,  M.  de,  ou  the  succession  of  spe- 
cies, 3(M. 
Artichoke,  Jerusalem.  110. 
Ascension,  plants  of,  :i55. 
Asclepias,  pollen  of,  185. 
Asparagus,  3.32. 
Aspicarpa.  .377. 
Asses,  striped,  101. 

improved  by  selection,  49. 
Atenchus,  140. 

Aucanitaine,  ou  land-shells,  301. 
Audubon,  on  habits  of  friL'ate-bird.  178. 

on  variation  in  birds'-nests,  204. 

on  heron  eating  seeds,  351. 
Australia,  animals  of,  113. 

dogs  of,  207. 

extinct  animals  of,  310. 

European  plants  in,  345. 

glaciers  of,  342. 
Azara,  on  flies  destroying  cattle,  78. 
Azores,  flora  of,  335. 

Babington,  Mr.,  on  British  plants,  57. 
Baer,  Von,  standard  of  Iliirnness,  122. 

comparison  of  bee  and  fish,  314. 

embryonic  similarity  of  the  vertcbra- 
ta,  395. 
Balancement  of  growth,  149. 
Barbeny,  flowers  of,  100. 
BarrandV,  !M.,  on  Silurian  colonies,  296. 

on  the  succession  of  species,  205. 

on   parallelism  of  paleozoic  forma- 
tions, .307. 

on  afflnities  of  ancient  species,  308. 
Barriers,  importance  of,  .323. 
Bates,  Mr.,  on  mimetic  butterflies,  884. 
Batrachians  on  islands,  3.5S. 
Bats,  how  structure  acquired,  174. 

distribution  of,  3,")4. 
Bear,  catching  water-insects.  176. 
Beauty,  how  acquired,  194,  422. 
Bee,  sting  of,  197. 

queen,  killing  riv.nls,  197. 

Australian,  extermination  of,  81. 
Bees  fertilizing  flowers,  7'.). 

hiye,  not  sucking  the  red-clover,  97. 

Ligurian,  9S. 

hive,  cell-making  instinct,  216. 

variation  in  habits,  201. 


INDEX. 


439 


Bees,  humble,  cells  of,  217. 

parasitic,  212. 
Bcellpf",  wiiifriffn,  in  MadciM,  Ml. 

with  dcliciciit  tnri<i,  110. 
Dcutlinm,  ^Ir.,  on  Uritish  plants,  57. 

on  claeslQcation,  .'JTS. 
Berkeley,  Mr.,  ou  seeds  in  salt-water, 

a31. 
Bermuda,  birds  of,  357. 
Birds  acquirin*;  fear,  201. 

beauty  of,  I'JO. 

annually  eross  flic  Atlantic,  3.3C. 

color  of^  ou  continents,  l.'iS. 

footbteps,  and  remains  of,  in  eecouda- 
ry  rocks,  2SS. 

fossil,  In  caves  of  Brazil,  31C. 

of  Madeira,  Bermuda,  audCialapagos, 
a")((. 

8on<;  of  males,  01. 

transportiu!,'  seeds,  333. 

waders,  353. 

windless,  139,  17  k 
Bizcaeli.i,  .•}2l. 

atllniti.'s  of,  3S7. 
Bladder  for  swimmin?  in  fish,  183. 
Blinducss  of  cave  animals,  142. 
Blyth,  Mr.,  ou  distiuctuess  of  Indiau  cat- 
tle, 31. 

on  striped  hcmionus,  IGl. 

on  crossed  geese.  2."i!(. 
Borrow,  Mr.,  on  the  Spai'isli  pointer.  44. 
Bory,  St.  Vincent,  on  lial  i-icliijins,  ;35S. 
Bosquet,  M.,  on  fossil  Clitlininaltis,  2,S!). 
Bowlders,  erratic,  ou  the  ^Vzores,  333. 
Brauchioc,  1&3,  IRl. 

of  crustaceans,  187. 
Brancliiostoma,  123. 
Brent,  Mr.,  ou  liouso-tuinblera,  207. 
Britain,  mammals  of,  300. 
Bronu,    Prof.,  ou   duration    of  specific 
forms,  2711. 

Various  objections  by,  120. 
Brown,  Kobert,  on  classiiication,  .375. 

Seciuard,  on  iidieritod  epilepsy,  140. 
Buttcrllies,  mimetic,  ;iHl. 
Buzareingucs,  ou  sterility  of  varieties, 
25<J. 

Cabbajje,  varieties  of,  crossed,  101. 
Calceolaria,  237. 

Canary  birds,  sterility  of  hybrids,  2.38. 
Cape  do  Verde  islands,  productions  of, 
.3(i3. 

plants  of,  on  mountains,  311. 
Cape  of  (iood  Hope,  plants  of.  133,  355. 
Carpenter,  Dr.,  on  CKZonn,  291. 

on  foi-aminifcra,  313. 
Cafasetum,  189,  381. 
Cats,  with  blue  eves,  deaf,  26. 

variation  in  habits  of,  20,"). 

curlinj;  tail  wheu  jjoin;^  to   spring, 
19.S. 
Cattle  destroyin?  flr-trees,  78. 

destroyed  by  flies  in  Panirruay,  78. 

bn-eds  of,  locally  extinct,  KKI. 

fertility    of    Indian    and    European 
breeds,  2.39. 

Indian,  31.  2.!9. 
Cave,  iuhabitauts  of,  blind,  112. 


Cecidomyia,  SO."*. 

Celts,  proviuj;  antiquity  of  man,  31. 

Centres  of  creation,  32(i. 

Ccphalopodie,  development  of,  397. 

Cervulus,  2:58. 

Cetacea,  teeth  and  hair,  117. 

Cfvlon.  plants  of,  ;>l(i. 

Chalk  formation,  ;i03. 

Characters,  divergence  of,  110. 

sexual,  variable,  152. 

adaptive  or  analogical,  382. 
Charlock,  81. 
Checks  to  increase,  74. 

mutual,  77. 
Chickens,  instinctive  tamcncss  of,  208. 
(■Iithani;ilin;e,  273. 

Clithaiiialus,  cretaccan  species  of,  289. 
Circumstunees  favorable  to  selection  of 
domestic  products,  48. 

favorable  to  natural  selection,  103. 
Cirripcdes  capable  of  crossing,  102. 

carajjace  aborted,  150. 

their  ovigerous  freua,  183. 

fossil,  28.><. 

larvKi  of,  396. 
Clarke,  Rev.  W.  B.,  on  old  glaciers  in  Aus- 
tralia, 3t2. 
Clnpsifiealion,  372, 

('lilt.  -Mr.,  on  the  succession  of  types,  316. 
Climate,  eftecta  of,  in  checking  increase 
of  beings,  75. 

adaptation  of,  to  organisms,  111. 
Climbing  plants,  IS2. 
Clover  visited  by  b('es.  97. 
Cobites,  inti'stiiie  of,  182. 
Cockroacli,  81. 

Colleclicms,  jjaleontnloLrieal,  poor,  273. 
Color,  inllucnced  bv  eliiiiate.  138. 

in  relation  to  ail  icks  by  flies,  19.3. 
Columba  livia,  parent    of  domestic  pig- 
cons,  .35. 
Colymbetes,  353. 
Compensation  of  growth,  149. 
Compositic,  flowers  and  seeds  of,  129. 

outer  and  inner  florets  of,  148. 

male  flowers  of,  40(j. 
Conclusion,  general,  429. 
Conditions,  slitrht  changes  of,  favorable 

to  fertility,  253. 
Converp:ence  of  genera,  132. 
Coot,  177. 
Coral-islands,  seeds  drifted  to,  .3.33. 

reefs,  indicating  movements  of  earth, 
293. 
Corn-crake,  178. 

Correlated  variation  in  domestic  produc- 
tions, 25. 
Coryanthcs,  1.h8. 
Creation,  single  centres  of,  32C 
Criiium,  23fi. 

Croll,  Mr,  on  subaerial  denudation,  269, 
271. 

on  the  age  of  our  oldest  formatious, 
291. 

on  nlternnte  Glacial  periods   in  the 
north  and  south,  31.3. 
Crosses,  reciprocal.  213. 
Crossing  of    domestic   animals,   impor 
taucc  in  altering  breeds,  32,  33. 


440 


INDEX. 


Croseincr,  mlrantajrcs  of,  00. 

uiifiivorable  to  selection,  102. 
CrnETcr,  Dr..  on  Coryanthes,  18tj. 
Cnistacca  of  New  Zealand,  345. 
Crus'acenn,  blind,  \i'2. 

nir- breathers,  18tj. 
CryptocerujJ.  a-2>!. 
Ctenomvs,  blind,  1 11. 
t'lickoo,"  instinct  of.  200. 
("urrantp,  praftsof.  2-15. 
Currents  of  sea,  rale  of,  332. 
Cuvier,  on  conditions  of  existence,  200. 

on  foBsil  monkeys,  288. 

Frcfl.,  on  instinct,  201. 
Cyclostouia,  resisting  salt-water,  3C2. 

Dana,  Prof,  on  blind  cave-animals,  lt.3. 

on  relations  of  crustaceans  of  Japan, 
342. 

on  cnistaccans  of  New  Zealand,  345. 
Dawson,  Dr.,  on  cozoon,  202. 
Do  CandoUo,  Aujr.  Pyr.,  on  etnissle  for 
existence,  70. 

on  nmbelliferic,  140. 

<m  frcneral  affinities,  .388. 
Dc  Candolle,  Alpb.,  on  the  variability  of 
oaks,  GO. 

on   low     plants,    widely    dispersed, 
307. 

on  widely-ranging  plants  being  vari- 
able, ()•). 

on  naturalization,  113. 

on  winged  seeds,  149. 

on  Alpine  species  suddenly  becoming 
rare,  KiO. 

on  distribution  of  plants  with  large 
seeds,  3.32. 

on  vegetation  of  .\nstralia,  317. 

on  fresh-watvr  plants,  353. 

on  insular  i)lants,  .3.55. 
Degradation  ol  rocks.  269. 
Deuudatioii,  rate  of,  271. 

of  oldest  rocks,  202. 

of  granitic  areas,  277. 
Development  of  ancient  forms,  313. 
Devonian  system,  311. 
Dianthus.  fertility  of  crosses,  241. 
Dimorphism  in  plants,  .55,  253. 
Dirt  ou  feet  of  birds,  :i34. 
Dispersal,  means  of,  329. 

during  Glacial  period,  .3.37. 
Distribution,  geographical,  .322. 

means  of,  330. 
Disuse,  effects  of,  under  nature,  1.39. 
Divergence  of  character,  110. 
Diversification  of  means  for  same  general 

purpose,  ISO. 
Division.  physioloL'ical.  of  labor,  113. 
Dogs,  hairless,  with  imi)orfect  teeth,  26. 

descended  from  several  wild  slocks, 
32. 

domestic  instincts  of,  207. 

inherited  civilization  of.  207. 

fertility  of  breeds  together,  2.30. 

■  of  crosses,  a5<i. 

pmporticms    of    body    in    dlflferent 
breeds,  when  young,  399. 
Domestication,  variation  under,  22. 
Double  flowers,  227. 


Downing,  Mr.,  on  fmlt-trees  in  America, 

80. 
Dragon-flies,  intestines  of,  182. 
Drifi-timber.  32). 
Driver-ant.  2-30. 

Drones  killed  by  other  bees,  197. 
Duck,  domestic,  wings  of,  reduced,  25. 

logger-headed,  174. 
Duckweed.  352. 
Dugong,  affinities  of.  375. 
Dung-beetles  with  deficient  tarsi,  140. 
Dytiscus,  .353. 

Earl,  Mr.  W.,  on  the  Malay  Archipelago, 

3(X). 
Ears,  drooping,  in  domestic  animals,  26. 

rudimentary.  408. 
Earth,  seeds  in  roots  of  trees,  333. 

charged  with  seeds,  335. 
Eciton,  228. 

Economy  of  organization,  150. 
Edentata,  teeth  and  hair,  147. 

fossil  species  of,  318. 
Edwards,  Milne,  on  physiological  divis- 
ion of  labor,  122. 

on  gradations  of  structure,  190. 

on  cmbryological  characters,  378. 
Egsrs.  young" birds  escaping  from,  90. 
E'rypt.jiroductions  of,  not  modified,  125. 
Electric  organs,  184. 
Elephant,  irate  of  increase,  72. 

of  Glacial  period,  145. 
Embrj'ology,  394. 
Eozoon  Caiiadense,  201. 
Epilepsy  inherited,  140. 
Existence,  sfrngu'le  for,  CO. 

conditions  of,  200. 
Extinction,  as  bearing  on  natural  selec- 
tion, 114. 

of  domestic  varieties,  118. 

290. 
Eye,  stnictnre  of,  170, 

correction  for  aberration,  197. 
Eyes,  reduced  iu  moles,  1-12. 

Fabre,  M.,  on  hymenopfera  fighting,  91. 

on  parasitic  sphex,  212. 

on  sitaris,  402. 
Falconer,  Dr.,  on  naturalization  of  plants 
in  India,  73. 

on  elephants  and  mastodons,  311. 

and  Cautley,  on  mammals  of  snb-llim- 
alavan  beds,  317. 
Falkland"  Islands,  wolf  of,  359. 
Fanlts,  270. 
Faunas,  marine,  323. 
Fear,  instinctive,  in  birds.  208. 
Feet  of  birds,  young  mollusks  adhering 

to,  :K2, 
Fertilization  varionslv  effected,  188,  105. 
Fertility  ofhvbrids,  2.37. 

from  sliirlit  changes  in  conditions,  252. 
Fertility  of  crossed  varieties,  257. 
Fir-trees  dcstroved  by  cattle,  78. 

pollen  of,  198. 
Fish,  flying.  r.S. 

teleostean,  sudden  appearance  of,  290 

catini,'  seeds,  3.31,  .3.51. 

fresh-water,  distribution  of,  352. 


INDEX. 


441 


Fl8hcB,  canoid,  now  confined  to  frceh- 
wator,  107. 
electric  orirans  of,  ItC). 
ganoid,  living  in  frcHli-wntcr,  302. 
of  Boutlicrn  licminplu're,  'H'>. 
Flight,  powers  of,  liow  acquired,  17.5. 
P'liiit  tools,  provini;  antiquity  of  man,  31. 
Florida,  pi^'s  of,  89. 

FlowerH,    flrutiure    of,    in    relation    to 
crosfin}:.  95. 
of  composita;  and  umbellifene,  146. 
beauty  of,  195. 
double,  2*27. 
Flyech  formation,  destitute  of  organic  re- 

niaiuB,  273. 
Forbcp,  Mr.  D..  on  glacial  action  in  the 
Andes.  iU:i. 
E.,  on  colors  of  shells,  l.'Jft. 
on  abrupt  range  of  bliella  in  depth, 

lot. 

on  jioomess  of  palcontological  col- 
lections, 273. 
on  coutiuuous  succession  of  genera, 

29S. 
on  ronfinental  extension.  330. 
on  distribution  during  Glacial  period, 

:W7. 
on  parallelism  in  time  and  spnce,  370. 
Forests,  chanires  In.  in  America,  80. 
Formatiim,  Devonian,  311. 

Cambrian     with     monocotyledonous 
plant,  201. 
Formations,  Ihirkness  of,  in  Britain,  271. 

intermittent,  280. 
Formica  ntfesceiis,  212. 
sanguinea,  213. 
flava,  neuter  of,  220. 
Forms,  lowly  organized,  long-enduring, 

124. 
Frena,  ovi^crons.  of  cirripedea.  183. 
Fresh-water   productions,    dispersal   of, 

351. 
Fries,  on  species  and  large  genera  being 

clbsely  allied  to  other  species,  60. 
Frigate-bird,  178. 
Frogs  on  islands.  .S.W. 
Fruit-trees,  gradual  improvement  of,  -15. 
in  United  States,  SO. 
varieties  of,  acclimatized  in  United 
States,  110. 
Fuci,  crossed,  219. 
Fur,  thicker  in  cold  climates,  1.38. 
Furze,  395. 

Oalapasos  Archipclaco.  birds  of,  30C. 

productions  of,  302,  .304. 
Galeopitliccus,  174.  * 

tiame,  increase  of.  checked  by  vermin.  7.'. 
tiiirtner,  on  sterility  of  hyhrills,  2.3.5,  210. 

on  reciprocal  crosses.  212. 

on  crossed  maize  and  verbasrnm.  2.50. 

ou  com|)arison  of  hybrids  and  mon- 
trrels,  2(il. 
Oaudrj-,  Prof.,  on  Intermediato  genera  of 

rossil  mammals.  :i0s. 
Geese,  fertility  when  crossed,  2.39. 

upland.  177. 
fSeikle,  Mr.,  on  subaTrial  deiindation,269. 
3encalogy  important  in  claselflcation,  ii?0. 


Generations,  alternate,  304. 

GeolTrov  St.-llilaire,  on  balancement,  110. 

on  nonioloL'ODs  organs,  391. 

Isidore,    on    variability  of   repeated 
parts,  151. 

on  correlation,  in  monstrosities,  20. 

on  correlation,  147. 
GeoflVoy  .st.-llilaire,  Isidore,  on  variable 

parts  being  oltcn  monstrous,  155. 
Geographical  distribution,  322. 
Geograpliy,  ancii'iit,  4;i5. 
Geology,  future  iirogrees  of,  435. 

imperfection  of  the  record,  200. 
GiraflTc,  tail  of,  191. 
Glacial  period.  3.37. 

aflfecling  the  North  and  South,  450. 
Gmelin,  on  dii^tribution,  .337. 
Godwin-Austen.  Mr.,  ou  the  Malay  Archi- 
pelago, 284. 
Goethe,  on  compensation  of  growth,  142 
Gomphia.  131. 
Gooseberry,  grafts  of.  245. 
Gould,  Dr.  Aug.  A.,  on  land-shells,  301. 

Mr.,  on  colors  of  birds.  l:}8. 

on  instincts  of  cuckoo,  211. 

on  distribution  of  genera  of  birds,  .300. 
Gourds,  crossed,  250. 
Graba,  on  the  Uria  lacrymans,  94. 
Grafts,  capacity  of,  245. 
Granite,  areas  of  denuded,  277. 
Grasses,  varieties  of,  112. 
Gray,  Dr.  Asa,  on  the  variability  of  oaks, 
00. 

on  man  not  causing  variability,  81. 

on  sexes  of  the  holly,  97. 

on  trees  of  United  States,  101. 

ou  naturalized  plants  in  the  United 
States.  113. 

on  wstivation.  130. 

on   rarity  of  intermediale  varieties, 
170. 

on  Alpine  plants.  337. 

Dr.  J.  E.,  on  stripeil  mule,  10;5. 
Grebe,  177. 

CJroups,  aberrant,  .387. 
Grouse,  colors  of,  88. 

red,  a  doubtful  species.  58. 
Growth,  compensation  of,  149. 
Giiuther,  Dr.,  on  the  lishcs  of  Panama,  323. 

Haast.  Dr.,  on  glaciers  of  New  Zealand, 

:i42. 
nabit.  effect  of.  nnder  domestication,  25. 
effect  of.  under  nature.  13!). 
diversitled,  of  same  species,  17.5. 
Iliickel,  Prof.,  on  classiflcation  and  the 

lines  of  descent,  :«)0. 
Tlairand  teeth,  correlated.  147. 
llarcourt,  Mr.  E.  V.,on  birds  of  Madeira, 

:J57. 
IlartunL'.  M.,  on  bowlders  in  the  Azores, 

3;i5. 
Hazel-nuts.  .3.31. 

Hearne,  on  habits  of  bears,  170. 
Ili-ath.  clmntes  in  veL't'lation,  77. 
lleer  Oswald,  on  ancient  cultivated  plant.s 

80. 
on  plants  of  Madeira,  100. 
Ileliiuithemum,  131. 


442 


INDEX. 


Helix  pomalia.  Hfil. 

Ili'loscmdium,  3.T.J. 

Ilciniomis.  eiriix'd,  KIO. 

Herhort,  W..  on  stru£ri.'Io  foroxistencc,  70. 

on  Picrilitv  of  hybrids.  2.3(5. 
ITccior,  Dr.,  on  glaciers  of  New  ZcaLind, 

llormaphroditcs  cropiiinsr.  98. 
Ilclix,  res>i*tin','t^nlt-\vater,  361. 
Heron  enlin^  seed,  .354. 
Heron,  Sir  K.,  on  peacockp.  92. 
Heusinsrer.  on  white  animals  poisoned  by 

certain  plant?,  2(5. 
Hewitt.  Mr.,  on  sterility  of  first  crosses, 

249. 
Hildcbrand.  Prof.,  on  the  self-sterility  of 

Corvdalis,  2;«. 
Hilprcndorf,  on  intermediate  varieties,  278. 
Himalaya,  jrlaciors  of,  342. 

plants  of,  .34.1. 
Hippeastrnm,  2-37. 
Hollv-trees,  sexes  of,  9<>. 
Hooker,  Dr..  on  trees  of  New  Zealand,  101. 

on     acclimatization     of    Himalayan 
trees,  144. 

on  flowers  of  umbellifene,  148. 

on  placiers  of  Himalaya,  342. 

on  alpc  of  New  Zealand.  34."i. 

on  ve^'ctation  at  the  base  of  the  Him- 
alaya, 3-l(;. 

on  plants  of  Tierra  del  Fiiecro,  3+1. 

on  Australian  plants,  31(),  .3(1'!. 

on  relations  of  flora  of  .America,  347. 

on  flora  of  the  Antarctic  lands,  349, 
.303. 

on  the  plants  of  the  Galapagos,  357, 
302. 

on  glacicys  of  the  Lebanon,  342. 

on  uinn  not  causin<r  variability,  84. 

on  plants  of  mountains  of  Fernando 
Po,  345. 
Hooks  on  palms,  192. 

on  seeds  on  islands.  3.-)8. 
Hopkins,  Mr.,  on  denndation,  277. 
Hiirnbill,  remarkable  instinct  of,  232. 
Horns,  rudimentary.  408. 
Horse,  fcissil,  in  L.a"  Plata,  299. 
Horses  destroyed  l)y  flies  in  Paraguay,  78. 

striped.  102. 

projiortions  of,  ivhen  young,  .399. 
Horticulturists,  selection  "applied  by,  42. 
Huber,  on  cells  of  bees,  221. 

P..  on  reason  blended  witli  instinct, 
201. 

on  habitual  nature  of  instincts,  202. 

on  slnye-makiiig  ants,  212. 

on  Melipona  doniestica,  217. 
Humble-bees,  cells  of,  217. 
Hunter,  J.,  on    secondary  sexual   char- 
acters, 152. 
HuKon,  Captain,  on  crossed  geese,  239. 
Huxley,  Prof.,  on  stnicture  of  hermaph- 
rodites, 102. 

on  forms  connecting  birds  and  rep- 
tiles, .308. 

on  homologous  organs,  394. 

on  I  lie  development  of  aphis,  398. 
Hybrids  and  mongrels  compared,  260. 
Hybridism,  2;«. 


Hydra,  slructnre  of,  182. 
Hymenoptera,  fighting,  91. 
Hymenopterous  insect,  diving,  177. 

Hila,  150. 

Icebergs  transporting  seeds,  3.35. 
Increase,  rate  of,  71. 

Individuals,  numbers  favorable  to  se.ec 
tion,  103. 

many,  >vhether  simultaneously   cre- 
ated, .329, 
Inheritance,  laws  of,  27. 

at  corresponding  ages.  27.  89. 
Insects,  color  of,  fitted  for  habitations,  88. 

sea-side,  colors  of,  138. 

blind  in  caves,  142. 

luminous,  185, 

neuter,  226. 
Instinct,  201. 

not    varying     simultaneously    with 
strncture,  223, 
Instincts,  domestic,  205. 
Intercrossing,  advantages  of,  98. 
Islands,  oceanic,  35.5. 
Isolation  favorable  to  selection,  104. 

Japan,  productions  of,  342. 

Java,  plants  of,  .345. 

Jones,  Mr.  J.  M.,  on  the  birds  of  Ber- 
muda. .357. 

Jourdain,  M..  on  the  eve-spots  of  star- 
fishes, 179. 

Jukes,  Prof.,  on  subaerial  denudation, 
2<i9. 

Jnssieu,  on  classification,  ,377. 

Kentnckv,  caves  of.  142. 
Kercuelen-land,  flora  of,  349,  3^3. 
Kidney-bean,  acclimatization  of,  146. 
Kidneys  of  birds.  141. 
Kirby,  on  tarsi  deficient  in  beetles,  140. 
Knight,  Andrew,  on  cause  of  variation, 

22, 
KOlreuter,  on  the  barberry,  100. 

on  sterility  of  hybrids.  2.34. 

on  reciprocal  crosses,  242. 

on  crossed  varieties  of  nicotiana,  2.')9. 

on  crossing  male  and  hermaphrodite 

flowers,  405. 

Lamarck,  on  adaptive  characters,  383. 
Laucelet,  12.3. 

eves  of,  ISO. 
Land-shells,  distribution  of.  361. 

of  Madeira,  naturalized.  305. 

resisting  salt-water.  362. 
Languages,  classification  of,  380. 
Lapse,  great,  of  time,  268. 
Larrip,  396. 

Laurel,  nectar  secreted  by  the  leaves,  95. 
Lanrentiau  foi-mation.  291. 
Laws  of  variation.  137. 
Leech,  varieties  of,  81. 
Leguniinoste,  nectar  secreted  by  glands, 

95. 
Leibnitz's  attack  on  Newton,  430. 
Lepidosircn,  107.  308. 

limbs  in  a  nascent  condition,  406. 


INDEX. 


443 


Lcwcs,  Mr.  G.  II.,  ou  the  Salamandra atra, 
405. 
on  many  forms  oTlifc  having  been  at 
flrnt  evolved,  -i:}-.'. 
Life,  Ptriit,'L'lc  lor,  70. 
Linf,'ula,  .Silurian,  290. 
LinuiruH,  aphorism-of,  371. 
Lion,  mane  of,  91. 

vonnjj  of,  striped,  095. 
Lobelia  ful;,'ens,  79.  1(K).  .   . 

Lobelia,  sterility  of  crosses,  2.17. 
LoeuKtf".  transport  in;;  seeds,  331. 
Lo;;au,  Sir  W.,  ou  Laurentian  formation, 

292. 
Lowe,  IJev.  R.  J.,  on  locusts  visiting  Ma- 
deira, XU. 
Lowncss  of  Btrncture  connected  with  vari- 

abillly.  151. 
Lowncss,  related  to  wide  distribution, 

3(i7. 
Lubboek,  Sir  J.,  on  the  nerves  of  coccus, 
51. 
on  seeondary  sexual  characters,  157. 
on  a  divini,'  li  vmenoptcrous  insect,  177. 
on  aninitics,"2HS. 
on  nu'taniorpho-es.  .391,  .390. 
Lucas,  Dr.  P..  on  inherit.nncc,  27. 

on  resemblance  of  child  to  parent.  2(J-3. 
Lund  and  Clausen,  on  fossils  of  Brazil, 

MH. 
Lyell,  Sir  C,  on  the  stniggle  for  exist- 
ence, 70. 
on  modem  changes  of  the  earth,  98. 
ou  a  carboniferous  land-shell,  274. 
on    strata  beneath  Silurian  system, 

291. 
on  the  imperfection  of  the  geological 

record,  291. 
on  the  appearance  of  species,  294. 
on  Barrande's  colonies,  29f). 
on  tertiary  formations  of  Knropc  and 

North  .\merica,  303. 
on  i)arallelism  of  tertiary  formations, 

307. 
on  transport  of  seeds  by  icebergs.  335. 
on  great  alternationH  of  climate,  ;J50. 
on   the    distribution   of   fresh-water 

shells,  a-)3. 
on  land-shells  of  Madeira,  STto. 
Lvcll  and  Dawson,  on  fossilized  trees  in 

Nova  Scotia,  2H1. 
Lythrum  salicaria  trimoqihic,  255. 

Macleay,  on  analogical  characters,  ;jfl3. 
^IcDonni'll,  Dr.,  on  electric  organs,  181. 
JIadcira,  jilaiits  of,  1(»7. 

beetles  of,  wingless,  110. 

fos^.il  land-shells  of,  317. 

birds  of,  ;i57. 
Magi)ie,  tame,  in  Norway,  205. 
Males  ngliting.  91. 
Maize,  crossed.  258. 

Malay  .\rchipelago  compared  with  Eu- 
rope, 2H1. 

mammals  of.  .3*!0. 
Malpighiacea>,  small  imperfect  flowers  of, 
12'J. 

377. 
Mammn,  rudimentary,  405. 


Mammals,  fossil,  in  secondary  formation, 
288. 

insular,  3.59. 
Man,  origin  of  races  of.  193. 
Manatee,  rudimentary  nails  of,  408. 
Marsupials  of  .Vustralia,  113. 

fossil  species  of,  316. 
Martens.  ^1..  experiment  on  seeds,  332. 
Martin,  Mr.  W.  C,  on  striped  mules,  163 
Masters,  Dr.,  on  Sanonaria,  131. 
Matteucci,  ou  the  electric  organs  of  rays 

187. 
Matthiola,  reciprocal  crosses  of,  212. 
Means  of  dispersal,  .331. 
Melipoiia  domestica,  217. 
^IiTrell,  Dr.,  on  tlie  American  cuckoo,  209. 
M(tiiinori)liism  of  oldest  rocks,  292. 
>lice  destroying  bees,  80. 

accliinafizaticm  of.  14.5. 
Miller.  Prof.,  on  tlie  cells  of  bees,  218,221. 
Mirabilis,  erot^ses  of,  242. 
Missel-tlimsh,  81. 
Mistletoe,  complex  relations  of,  19. 
Mockiiig-tlirnsli  of  the  Galapagos,  ;)66. 
Modification  of  species,  how  far  applica- 
ble. 431. 
Moles,  blind,  141. 
Mongrels,  fertility  anil  sterility  of,  256. 

and  hybrids  compared,  200. 
Monkeys,  fossil,  2.S.S. 
ISIonachauthus.  381. 

Mons  Van,  on  the  origin  of  fruit-trees,  .39. 
Monstrosities,  52. 

Monquin-Tandon,  on  sea-side  plants,  1.38. 
MorplioloL'v.  .31)0. 
Mozart,  musical  powers  of,  202. 
Mud,  seeds  in,  ,3.M. 
Mules,  striped,  163. 

Muller,  Dr.  Ferdinand,  on  Alpine  Aus- 
tralian plants,  352. 
Miiller,  Fritz,  on  dimorphic  crustaceans, 
55,  230. 

on  the  lancelet,  124. 

on  air-breathinir  crustaceans,  1S6. 

on  the  self-sterility  of  orchids,  2.37. 

on  embryology  in  relation  to  classifi- 
cation ,378. 

on  the  metamorplioscs  of  crustaceans, 
398.  403. 

on  terrestrial  and  fresh-water  organ- 
isms not  undergoing  any  metamor- 
phoses, 401. 

on  the  metamorphoses  of  insects,  402. 
Multiplication,  indetlnife,  of  species,  132. 
Murchison,  Sir  K.,  on  the  formations  of 
liussia.  274. 

on  iizoic  formations,  291. 

on  extinction,  2'.>9. 
Murray,  Mr.  A.,  on  cave-insects,  143. 
-Mustela  vision,  173. 
Myan  thus.  381. 
Myrmecocystus.  22-''. 
Myrmica,  eyes  of,  229. 

Nilgeli,  on  morphological  characters,  129. 
Nails,  rudimentary,  40.S. 
Nathusius,  Von,  rm  pigs,  19.3. 
Natural  history,  future  progress  of,  4;J3. 
selucliou,  hi. 


444 


INDEX. 


Kat.iirnl  pvptom,  374. 

Is'atunilizntion  of  forms  distinct  from  tlie 
iii(lif;ei)0U8  species,  ll.'J. 

in  New  Zealand,  l'.»7. 
Naudin,    on     analof,'ou3    variations    in 
gourds,  15'.t. 

on  hyhrid  f^ourds,  S259. 

on  reversion,  'M. 
Nantilus,  Sihirian,  290. 
Nectar  of  plants,  il.j. 
Nertaries,  how  formed,  93. 
Nelumbinm  lutenm,  :io4. 
Nests,  variation  in,  204,  22o,  2.31. 
Neuter  insects,  22(i. 
Newman,  Colonel,  on  hnmble-hees,  79. 
New  Zealand,  productions  of,  not  per- 
fect, 197. 

naturalized  products  of,  315. 

fossil  birds  of.  .317. 

placiers  of,  .342. 

cnistaceans  of,  345. 

alpn  of,  315. 

number  of  plants  of,  355. 

nora  of,  363. 
Newton.  Sir  I.,  attacked  for  irrelip;ion,  429. 

Prof,    on    earth  attached  to  a  par- 
tridge's foot,  .3.35. 
Nicotiana,  cros-ed  varieties  of,  2fi0. 

certain  species  very  sterile,  242. 
Noble,  Mr.,  on  fertility  of  Rhododendron, 

237. 
Nodules,  phosphatic,  iu  azoic  rocks,  291. 

Oaks,  variability  of  fiO. 

(Enonis,  small  imperfect  flowers  of,  129. 

Onites  ap|)elles,  1 10. 

Orchestia,  dimorphic,  .5.5. 

Orchids,  fertilization  of,  188. 

forms  of,  381. 
Orchis,  pollen  of,  1S.5. 
Oriranization,  tendency  to  advance,  121. 
Orjjans  of  extreme  perfection,  178. 

electric,  ofllshes,  18.5. 

of  little  importance,  190. 

homoloijous.  391. 

nidimcnts  of,  and  nascent,  4W. 
Ornithorhynchus,  107,  3T(i. 
Ostrich  not  capable  of  lliirht,  140. 

habit  of  laying  eggs  together,  212. 

American,  two  species  of,  321. 
Otter,  habits  of.  how  acquired,  173. 
Ouzel,  water,  17fi. 
Owen,  Prof,  on  birds  not  flying,  139. 

on  vegetative  repetition",  151. 

on  variability  of  unusually  developed 
parts,  152. 

on  the  eyes  ofllshes,  ISO. 

on  the  swim-bladder  ofllshes,  1S3. 

on  the  brancbiie  ofcirripedes,  183. 

on  electric  organs.  181. 

on  fossil  horse  of  La  Plata,  300. 

on  relations  of  ruminants  and  pachy- 
derms, 307. 

on  fossil  birds  of  New  Zealand,  317. 

on  succession  of  types,  31R. 

on  alliiiities  of  the  dugong,  374. 

on  homologous  organs,  391. 

on    the   mclamorphoaU  of  ccphalo- 
pods,  397. 


Pacific  Ocean,  fannas  of,  .32'1. 

Pacini,  on  electric  organs,  ls,5. 

Paley,  on  no  organ  formed  to  give  pain, 

190. 
Pallas,  on  the  fertility  of  the  domesticated 

descendants  of  wild  stocks,  239. 
Palm  with  books,  l!^i 
Paraguay,  cattle  destroyed  by  flics,  78. 
Parasites,  212. 
Partridge,  with  ball  of  earth  attached  to 

foot,  .331,  .3.35. 
Parts  greatly  developed,  variable.  152 
Parus  major.  176. 
Passiflora,  2:30. 
Peaches  in  United  States,  89. 
Pear,  grafts  of  2-15. 
Pelargonium,  flowers  of,  148. 

sterility  of,  237. 
Pelvis  of  women,  147. 
Peloria,  148. 
Period,  glacial,  .3:57. 
Petrels,  habits  of,  177. 
Phasianus,  fertility  of  hybrids,  239. 
Pheasant,  young,  wild,  208. 
Phillips,    Prof,    on   fresh-water    shells, 

.314. 
Pictct,  Prof.,  on  groups  of  species  sud- 
denly appearing,  286,  287. 

on  rate  of  organic  change,  296. 

on  continuous  succession  of  genera, 
298. 

on  change  in  latest  tcrtiory  forms,  282. 

on  close  alliance  of  fossils  in  consec- 
utive formations,  312. 

on  early  transitional  links,  287. 
Pierce,  Mr.,  on  varieties  of  wolves.  93. 
Pigeons  with  feathered  feet  and  skin  be- 
tween toes.  26. 

breeds  described,  and  origin  of,  3.3. 

breeds  of,  how  produced,  46,  49. 

tumbler,  not  being  able  to  get  out  of 
cgc:.  90, 

reverting  to  blue  color.  161. 

instinct  of  tumbling,  207. 

young  of,  399. 
Pigs,  black,  not  aflected  by  the  paint- 
root,  26. 

modified  by  want  of  exercise,  193. 
Pistil,  rudimentary,  105, 
Plants,  poisonous",  not  affecting  certain 
colored  animals,  26. 

selection  applied  to,  42. 

gradual  improvement  of.  45. 

not  improved  in  barbarous  countries, 
46. 

destroyed  hy  insects,  75. 

dimorphic,  55,  2,5;J. 

in  midst  of  range,  have  to  strugijla 
with  other  plants,  82. 

nectar  of,  95. 

fleshy,  on  sea-shores,  138. 

climbing,  182. 

fresh-water,  distribution  of,  .35.3. 

low  in  scale,  widely-distributed,  307. 
Plumage,  laws  of   change    in  sexes  of 

birds,  92, 
Plums  in  the  United  Slates,  89. 
Pointer  dog.  origin  of,  44. 

habits  of,  207. 


INDEX. 


445 


Poison  not  nfTccting  certain  colored  nni- 

nialn.  'X. 
eimilar   effect   of,    on    animals    and 

plants,  -IIK. 
Pollen  of  flr-treea,  198. 

transported  by  various  means,  188, 

1!)5. 
Pool,  Colonel,  on  striped  hcmionns,  162. 
Potamoireton.  :V>1. 
PreBlwich.  Mr.,  on  Knijlisli  and  French 

eocene  formations,  .'JUO. 
Proctotrupes,  177. 
Proleolepas,  150. 
Protens,  1 13. 
Tsycbology,  future  progress  of,  4;3C. 

Quap^a,  striped,  16.3. 
(Jnerens,  variability  of,  CO. 
Quince,  grafts  of,  245. 

Rabbit,  disposition  of  young,  207. 
Kiices,  domestic,  characters  of,  29. 
Kace-horses,  .\n»b,  4-1. 

English,  329. 
Hamond,  on  ])lants  of  Pyrenees,  S3f<. 
lliimsay.  Prof.,  on   suba'erial  denudation, 
209. 

on  thickness  of  the  British  forma- 
tions. 271. 

on  faults,  270. 
Kamsay.  Mr.,  ou  instincts  of  cuckoo,  282. 
Ratio  of  increase,  71. 
Itats  supplant ini:  each  other,  81. 

acclimatization  of,  145. 

blind  in  cave,  142. 
Rattlesnake,  19«. 
Reason  and  instinct,  201. 
Recapitulation,  general,  412. 
Reciprocity  of  crosses,  242. 
Record,  gcoloirical,  imperfect,  2fi6. 
Reng^rer  on  (lies  destroying  cattle,  78. 
Jti'produclion,  rate  of,  71. 
Resemblance  to  parents  in  mongrels  and 

hybrids,  2(jl. 
Reversion,  law  of  inheritance,  28. 

in  i)igeons  to  blue  color.  100. 
Rhododendron,  sterilitv  of,  2.'J.S. 
Itichard,  Prof.,  on  Asp{caii)a.  377. 
Richardson,     Sir.    J.,    on    structure    of 
squirrels.  173. 

on  llshes  of  the  southern  hemispliere, 
3t5. 
Robinia,  grafts  of,  245. 
Rodents,  blind.  141. 

Roi.'ers.Pri»r.,Mnp  of  North  America,  277. 
Itudimentarv  organs,  404. 
Rudiments  iuiportuut    for  classification, 

37C. 
RQtimeyer,  on  Indian  cattle,  31,  239. 

Balnmandm  atra,  405. 

Saliva  used  in  nests.  225. 

Sageret  on  grafts,  245. 

Salmons,    males,  fighting,    and    hooked 

jaws  of,  91. 
Salt-water,  how   far  injurious  to  seeds, 

3.32. 
not  destructive  to  landehells,  SCI,  3C2. 


Salter,  Mr.,  on  early  death  of  hybrid  cm 

bryos,  249. 
Sanrophagus  suli)hnrntiis,  17(>. 
Schiodte,  on  blind  insects,  112. 
Schlegel,  on  snakes,  147. 
Scott,  J.,  Mr.,  on  the  self-sterility  of  or- 
chids, 2.37. 

on  the  crossing  of  varieties  of  ver 
bascnm,  2.59. 
Sea-water,  how  far  injurious  to  seeds.  332. 

not  destructive  to  land-shells,  361,  .362. 
Sebright,  Sir  J.,  on  crossed  animals,  32. 
Sedgwick,  Prof.,  on  groups  of  species 

suddenly  appearing,  2,sC. 
Seedlings  destroyed  by  insects,  74. 
Seeds,  nutriment  in,  82. 

winged,  149. 

means  of  dissemination,  187, 194,  2.34. 

powers  of  resisting  salt-water,  3.32. 

in  crops  and  intestines  of  birds,  333. 

eaten  by  fish,  334,  355. 

in  mud,  353. 

hooked,  on  islands,  358. 
Selection  of  domestic  products.  40. 

principle  not  of  recent  origin,  4.3. 

unconscious,  43. 

natural,  84. 

eexnal,  90. 

objections  to  term.  85. 

natural,  has  not  induced  sterility, 2-16. 
Sexes,  relations  of,  90. 
Sexual  characters  variable,  156. 

selection,  90. 
Sheep,  Merino,  their  selection,  41. 

two  sub-breeds  unintentionally  pro- 
duced, 44. 

mountain,  varieties  of,  81. 
Shells,  color  of.  ViS. 

hinges  of,  188. 

littoral,  seldom  embedded,  273. 

fresh-water,    long    retjiin    the    same 
forms,  .314. 

fresh-water,  dispersal  of,  353. 

of  Madeira.  3.'J7. 

land,  distribution  of,  ^58. 

land,  resistin'T  salt-water,  .361,  .362. 
Silene,  infertility  of  crosses,  241. 
Silliman,  Prof.,  on  blind  rat.  142. 
Sitaris,  metamorphosis  of,  402. 
Skulls  of  young  mammals,  192,  303. 
Slave-makiiiir  instinct,  212. 
Smith,  Col.  Hamilton,  on  striped  horses, 
163. 

Mr.  Fred.,  on  slave-making  ants,  214. 

on  neuter  ants.  229. 
Snake  with  tooth  for  cutting  through  egg- 
shell, 212.  ^     ^^ 
Somerville,  Lord,  on  selection  of  slicep, 

41. 
Sorbns,  grafts  of,  215. 
Spaniel. "King  Charles's  breed,  44, 
Specialization  of  organs.  121. 
Species,  polymorphic,  M. 

dominant,  M. 

common,  variable,  62. 

in  large  grneni  variable.  Gt. 

groups  of,   suddenly  ap|)earing,  28G 
289. 

beneath  Silurian  formations,  291. 


440 


INDEX, 


Species  Hnccci'sivi-ly  appearinjr,  205. 

clmn^'ini;  riiinultaneously  tliroii'^hout 
the  world,  M-i. 
Ppenccr,  Lord,  on  increase  in  size  of  cat- 
tle, 44. 
Ucrbcrt.  Mr.,  on  the  first  steps  indif- 

feri'ntialion,  liO. 
Mr.  II.,  on  tin?  tendency  to  an  equi- 
librium in  all  forces,  252. 
Sphex,  parasitic,  212. 
Spiders,  development  of.  .3^7. 
Spilz-doi;  crossed  with  fox,  2o7. 
Sports  in  plants,  25. 
Sprengel,  C.  C,  on  crossing,  100. 

on  ray-florets,  118. 
Squirrels,  sradafions  in  structure,  174. 
Si;ifri)rdsliirc,  heath,  changes  iu,  77. 
Stag-beetles,  fighting.  91. 
Star-fishes,  eyes  of,  179. 
Sterility  from  changed  coaditions  of  life, 
2i. 
of  hybrids,  ?.3.3. 

'    ,  laws  of,  240. 

,  causes  of,  246. 

from  unfavorable  conditions,  251. 
not  induced   through  natural  selec- 
tion, 2ir,. 
S;.  Helena,  productions  of,  350. 
St.-Ililaire,  Aug.,  variability  of  certain 
plants,  i:50. 
on  classification,  377. 
St.  John,  Mr.,  on  habits  of  cats,  205. 
Sting  of  bee,  197. 
Slocks,  aboriginal,  of  domestic  animala, 

32. 
Strata,  thickness  of.  in  Britain,  271. 
Stripes  on  horses,  162. 
Structure,  degrees  of  utility  of,  19 1. 
Straggle  for  existence,  69. 
Succession,  geological,  295. 
Succession  of  types  in  same  areas,  316. 
Swallow,  one    species    supplanting   an- 
other, 81. 
Swifts,  nests  of,  225. 
Swim-bladder,  183. 
Switzerland,  lake  habitations  of,  31. 
System,  natural,  374. 

Tail  of  giraffe,  191. 

of  atpuitic  animals,  191. 

rudinientarv,  408. 
Tanais,  dimorpliic,  55. 
Tarsi  deliciciit.  1  li). 
T.Miscli,  on  umlu'lliferjc,  129. 
Tectli  and  l.nir  correlated,  147. 

rudimentary,  in  embryonic  calf,  406. 
428. 
Tciretmeier,  Mr.,  on  cells  of  bees,  219,  223. 
Temminrk  on  distribution,  aiding  classi- 

llcation.  378. 
Thompson,  Sir  W.,  on  the  age  of  the  hab- 
itable world,  272,  2tW. 
Thoiiin,  on  grafts,  215. 
Thrush,  aquatic  species  of,  177. 

mocking,  of  the  (}alai)agos,  366. 

young  of.  spotted,  395. 

nest  of,  232. 
Thuret,  M.,  on  crossed  faci.  242. 
Thwalles,  Mr.,  on  acclimatization,  144. 


Tierra  del  Fuego,  dogs  of,  207. 

plants  of,  .319. 
Timber-drift,  a33. 
Time,  lapse  of,  268. 

by  itself  not  causing  modification,  10.5. 
Titmouse,  176. 
Toads  on  islands,  358. 
Tobacco,  crossed  varieties  of,  259. 
Tomes,  Mr.,  on  the  distribution  of  bats, 

360. 
Torell.  on  a  monocotyledonous  Cambrian 

plant,  291. 
Transitions  in  varieties  rare,  168. 
Trautschold,  on  intermediate  varieties, 

279. 
Trees  on  islands  belonging  to  peculiar 
orders,  :J57. 

with  separated  sexes,  101. 
Trifolium  pratense,  79,  97. 

incamatum,  97. 

Trigonia,  302. 

Trilobites.  290. 

sudden  extinction  of.  302. 
Triraorphism  in  plants,  55,  253. 
Troglodytes,  232. 
Tuco-tuco,  blind,  141. 
Tumbler,  pigeons,  habits  of,  hereditary, 
207. 

young  of,  400. 
Turkey-cock,  tuft  of  hair  on  breast,  92. 

nakotl  skin  on  head,  192. 

young  of,  instinctively  wild.  208. 
Turnip  and  cabbage,  analogous  variationa 

of,  159. 
Type,  unity  of,  200. 
Types,  succession  of,  in  same  areas,  316. 

Udders  enlarged  by  use,  25. 

rudimentary,  405. 
nex,  young  leaves  of,  395. 
Umbeilifene,  flowers  and  seeds  of,  129. 

outer  and  inner  florets  of,  148. 
Unity  of  type,  200. 
Uria  lacrymans,  94. 
Use,  effects  of.  under  domestication,  26. 

eflVcts  of,  iu  a  state  of  nature,  139. 
Utility,  how  far  important  in  the  con- 
struction of  each  part,  193. 

Valenciennes  on  fresh-water  fish,  352. 
Variability  of  mongrels  and  hybrids,  260. 
Variation  under  domestication,  22. 

caused  by  reproductive  system  being 
afTected  by  conditions  of  life,  23. 

under  nature,  52. 

laws  of,  137. 

correlated,  25. 1 16,  194. 
Variations  appear  at  corresponding  ages, 
27,  89. 

analogous  in  distinct  speciea,  15S. 
Varieties,  natural,  52. 

struggle  between,  SO. 

domestic,  extinction  of,  109. 

transitional,  rarity  of,  168. 

when  crossed,  fertile,  257. 

when  crossed,  sterile,  256. 

classification  of,  381. 
Verbascum.  sterility  of.  2.37. 
Vcrbascum,  varieties  of,  crossed,  259. 


INDEX. 


447 


Verlot,  M.,  on  double  stocks,  227. 
Vcnieul,    M.  dc.  on    the    succession  of 

species,  ;J04. 
Viola,  email  imperfect  flowers  of,  129. 

tricolor,  7!t. 
Vlrcliow,  on  the  structure  of  the  crj-stal- 

line  lens,  l!>(). 
Volcanic  islands,  denudnllon  of.  270. 
Vulture,  naked  skin  on  head,  l!t2. 

Wadincr-birds,  .3,'J.3. 

Wagner,  Moriiz,  on  the  importance  of  iso- 
lation, 105. 
on  Cecidoniyia,  .3M. 
Wallace,  Mr.,  on  ori^'in  of  species,  17. 
on  the  limit  of  variaiiou  under  do- 
mestication, 50. 
on  laws  of  gcojjraphical  distribution, 

32!t. 
on  the  Malav  .Vrchtpela^o,  HOO. 
on  dimorj)hic  Icpidopterji,  55,  2.30. 
on  races  in  the  Malay  Archipelago,  57. 
on  mimetic  animals,  38(!. 
Walsh.  Mr.  B.  D.,  on  phytophagic  forms, 
58. 
on  equable  variability,  1.5ft. 
Water,  fresh,  productions  of,  351. 
Water-hen,  177. 

Waterhouse,  Mr.,  on  Australian  marsu- 
pials, 113. 
on  LTcatly-developcd  parts  being  vari- 
able, 152. 
on  the  cells  of  bees,  217. 
on  general  afflnities,  387. 
Water-ouzel,  177. 

Watson,  Mr.  II.  C,  on  range  of  varieties 
of  British  plants,  07. 
on  acclimatization,  111. 
on  tlora  of  Azores,  .33.5. 
on  Alpine  plants,  3.38. 
on   rarity  of  intermediate  varieties, 
170. 
.    on  convergence,  132. 
on  the    indefinite    multiplication  of 
species,  132. 
Weale,  Mr.,  on  locusts  transportingseeds, 

;m. 

Web  of  feet  in  the  water-birds,  177. 
Weismann,  Prof.,  on  the  causes  of  vari- 
ability, 2.3. 

on  morphological  characters,  127. 

on  nidiincntary  organs,  408. 


West-Indian  Islands,  mammals  of,  .360. 
Wcstwood,  on  species  in  large  genera  be- 
ing closely  allied  to  others,  (iO. 
on  the  tar^i  of  Kn-ridie,  ].")7. 
on  the  antenna;  of  hymeuopterous  in- 
sects, 375. 
Wheat,  varieties  of.  111. 
White  Mountains,  flora  of,  337. 
Whitlaker,  Mr.,  on  lines  of  escarpment, 

Wichura.Max.  on  hybrids,  250,  251,  261. 
Wings,  reduction  of  size,  140. 

of  insects  homologous  with  branchise, 

18;^. 
nidimentarv,  in  insects,  405. 
Wolf  crossed  w'ilh  dog,  200. 

of  Falkland  Isles,  35!). 
WoUaslon,  Mr.,  ou  varieties  of  insects, 
58. 
on  fossil  varieties  of  shells  in  Ma- 
deira, 62. 

on  colors  of  insects  on  sea-shore,  138, 
on  wingless  beetles,  141. 
on   rarity  of  intermediate  varieties 

170. 
on  insular  insects.  .3."5. 
on  land-shells  of  Madeira,  naturalized 
300. 
Wolves,  varieties  of,  0.3. 
Woodcock,  with  earth  attached  to  leg,  3.35, 
Woodpecker,  habits  of,  170. 

green  color  of,  102. 
Woodward,  Mr.,  on  the  duration  of  spe 
citic  forms,  279. 
on  the  continuous  succession  of  gen- 

era,  208. 
on  the  succession  of  tyjies,  317. 
World,  sijccios  changing  simultaneously 

throughout.  :j03. 
Wrens,  nest  of,  232. 

Wyniaii,  Prof.,  on  correlation  of  color  and 
eft'ect  of  pcison,  20. 
on  the  cells  of  the  bee,  218. 

Yonatt,  Mr.,  on  selection,  41. 
on  sub-breeds  of  sheep,  44. 
on  rudimentary  horns  in  young  cat- 
tle, 408. 

Zanthoxylon,  1,30. 
Zebra,  strii)e8  on,  102. 


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The  "  Lay  Sermons,  Addresses,  and  Reviews  "  is  a  book  to  be  read 
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There  are  those  who  hold  the  name  of  Professor  Huxley  as  synony- 
mous with  irreverence  and  atheism.  .  Plato's  was  so  held,  and  Galileo's, 
and  Descartes's,  and  Newton's,  and  Faraday's.  There  can  be  no  greater 
mistake.  No  man  has  greater  reverence  for  the  Bible  than  Huxley.  No 
one  more  acquaintance  with  the  text  of  Scripture.  He  believes  there  is 
definite  government  of  the  universe  ;  that  pleasures  and  pains  are  distrib- 
uted  in  accordaTice  with  law  ;  and  that  the  certain  proportion  of  evd 
woven  up  in  the  life  even  of  worms  will  help  the  man  -.rho  thinks  to  bear 
his  own  share  with  courage. 

In  the  estimate  of  Professor  Huxley's  future  influence  upon  science, 
Ills  youth  and  health  form  a  large  element.  He  has  just  passed  his  forty- 
fiflh  year.  If  God  spare  his  life,  truth  can  hardly  fail  to  be  the  gainer 
from  a  mind  that  is  stored  with  knowledge  of  the  laws  of  the  Creator's 
operations,  and  that  has  learned  to  love  all  beauty  and  hale  a.^  rileucss  of 
Nature  and  art. 


Works  of  Herbert  Spencer  puldialied  by  D.  Appktoii  d:  Co. 

ILLUSTRi.TIONS  OF  UNIVERSAL  PROGRESS. 

A  SERIES   OF  DISCUSSIONS. 

1  Vol     Larire  12mo.    470  FaRes.    Pxioe    (2.50. 


American  Notice  of  Spencer's  New  Sjstcm  of  Philosophy. 

L  Progress :  its  Law  and  Cause. 

II  Manners  and  Pashion. 

III.  The  Genesis  of  Science. 

IV.  The  Physiology  of  Laughter. 

V.  The  Origin  and  Function  of  Music. 

VL  The  Nebular  Ilj-pothesis. 

VIL  Baia  on  the  Emotions  and  the  Will. 

VIIL  Illogical  Geology. 

IX.  The  Development  Hypothesis. 

X.  The  Social  Organism. 

XL  Use  and  Beauty. 

XIL  The  sources  of  Architectural  Types. 

XIII.  The  Dbc  of  Anthropomorphism. 

These  Esstys  constitute  a  body  of  massive  and  original  thought  upon  a 
large  variety  of  important  topics,  and  will  be  read  with  pleasure  by  all  who 
appreciate  a  bold  and  powerful  treatment  of  ftmdamental  themes.  The 
gi.'neral  thought  which  pervades  this  book  is  beyond  doubt  the  most  iuipor 
tant  that  the  human  mind  has  yet  reached. — N.  Y.  Independent. 

Those  who  have  read  the  work  on  Education,  will  remember  the  ana- 
lytic tendency  of  the  author's  mind — his  clear  perception  and  admirable  ex- 
position of  lirst  principles — his  wide  gra.=p  of  facts — his  lucid  and  vigorous 
ityle,  and  the  constant  and  controlling  bearing  of  the  discussion  on  practical 
results.  These  traits  characterize  all  Mr.  Spencer's  writings,  and  mark,  m 
an  eminent  degree,  the  present  volume. — N.  Y.  IVibune. 

We  regard  the  distinguishing  feature  of  this  work  to  be  the  peculiarly 
Interesting  character  of  its  matter  to  the  general  reader.  This  is  a  groat 
literary  aa  well  as  pliiIo.«oi)hic  triumph.  In  the  evolution  of  a  system  of 
Philosophy  which  demands  serious  attention,  and  a  keen  exercise  of  the  in- 
tellect to  fathom  and  appreciate,  he  has  mingled  much  that  is  really  populof 
uid  entertaioing. — KocJuxlcr  DemocraL 


Wo)ks  of  Herbert  Spencer publislied  btj  D.  .dpptcton.  d-  Ob. 
A  NEW  SYSTEM  OF  PHILOSOPHY. 

FIRST    PPvINOIPLES. 

',  VoL    I^LTge  12mo.    515  Pages.    Price  $2  50. 

Contents : 
Part  Fikst. — llie  Unknowable. 

C/kiaptei  1.  Religion  and  Science;  II.  Ultimate  Religious  Ideas;  III 
DlUmatc  Scientific  Ideas;  IV.  The  Relativity  of  all  Knowledge;  V  Tht 
Reconciliation. 

Part  Secoxd  —  Laws  of  tlie  Knowable. 

I.  Laws  in  General;  II.  The  Law  of  Evolution;  III.  Tiie  same  con- 
tinued; IV.  The  Causes  of  Evolution;  V.  Space,  Time,  Matter,  Motion,  and 
Force ;  VI.  The  Indestructibility  of  Matter ;  VII.  The  Continuity  of  Motion ; 
VIII.  The  Persistence  of  Force ;  IX.  The  Correlation  and  Equivalence  of 
Forces;  X,  The  Direction  of  Motion  ;  XI.  The  Rhythm  of  Motion  ;  XII.  The 
Conditions  Essential  to  Evolution ;  XIII.  The  Instability  of  the  ilomoge- 
neous ;  XIV.  The  Multiplication  of  Eflects ;  XV.  Diflerentiation  -.nd  Inte- 
gration ;  XYI.  Equilibration ;  XVII.  Summary  and  Conclusion. 

In  the  first  part  of  this  work  Mr.  Spencer  defines  the  province,  limits,  and 
relations  of  religion  and  science,  and  determines  the  legitimate  scnpc  of 
philosophy. 

In  part  second  he  unfolds  those  fundamental  principles  which  have  been 
arrived  at  within  the  sphere  of  the  knowable ;  which  are  true  of  all  orders 
of  phenoncma,  and  thus  constitute  the  foundation  of  all  philosophy.  Tho 
law  of  Evolution,  Mr.  Spencer  maintains  to  be  universal,  and  he  has  hero 
worked  it  out  as  the  basis  of  his  system. 

These  First  Principles  are  the  foundation  of  a  system  of  Philosophy 
bolder,  more  elaborate,  and  comprehensive  perhaps,  than  any  other  which 
oat  been  hitherto  designed  in  England. — British  Quarterly  Ikview. 

A  work  lofty  in  aim  and  remarkable  in  executioa — CorrJiill  Mayannt. 

In  the  works  of  Herbert  Spencer  we  have  the  rudiments  of  a  positita 
Theology,  and  an  immense  step  toward  the  perfection  of  the  science  of  Psy- 
chology.— Christian  Examiner. 

If  we  mistake  not,  in  spite  of  the  very  negative  character  of  liis  own  r& 
toltB,  he  has  foreshadowed  some  strong  arguments  for  the  doctrine  of  a  po» 
lire  Christian  Theology. — New  Englanda: 

As  far  as  the  frontiers  of  knowledge,  where  the  hitcllect  may  go,  iJierc  li 
to   living   man   whose   guidance   may   more    safely   be   trusted. — AtUmtit 


Worki  o/  Herbert  Spencer  published  by  D.  AppUUm  d:  Co 


A   NEW  SYSTEM   OF  PHILOSOPHY. 

PKINCIPLES  OF  BIOLOGY. 

Tbifl  work  is  now  in  course  of  publication  in  quarterly  numbcre  (from  80 
to  100  pages  each),  by  subscription,  at  $2  per  annum.  It  is  to  form  two  vol- 
Bmes,  of  which  the  first  is  nearly  completed,  four  numbers  having  been 
jsued.  \Vhile  it  comprises  a  statement  of  those  general  principles  and  laws 
of  life  to  which  science  has  attained,  it  is  stamped  with  a  marked  originality» 
both  in  the  views  propounded  and  in  the  method  of  treating  the  subject.  Il 
will  be  a  standard  and  invaluable  work.  Some  idea  of  the  discussion  may 
be  formed  by  glancing  over  a  few  of  the  first  chapter  headin^rs. 

Part  Fikst. — Data  of  Biology. 

I.  Organic  Matter;  XL  The  actions  of  Forces  on  Organic  Matter;  III 
The  Reactions  of  Organic  Matter  on  Forces ;  IV.  Proximate  Definition  of 
Life ;  V.  The  Correspondence  between  Life  and  its  Circumstances ;  VI.  The 
Degree  of  Life  Varies  with  the  Dcgi'ce  of  Correspondence ;  VII  Scope  of 
Biology. 

Paut  Second. — I.vdcctions  of  Bior.oai. 

L  Growth;  IL  Development;  III.  Function;  IV.  Waste  and  Repait , 
V.  Adaptation;  VL  Individuality;  VIL  Genesis;  VIIL  Heredity;  IX. 
Variation;  X.  Genesis,  Ileredity,  and  Variation;  XI.  Classification;  XIL 
Distribution. 

Mr.  Spencer  is  equally  remarkable  for  his  search  after  first  principles; 
tat  his  acute  attempts  to  decompose  mental  phenomena  into  their  primary 
oemcnta ;  and  for  his  broad  generalizations  of  mental  activity,  mind  in  coi> 
nection  with  instinct,  and  all  tlie  analogies  presented  by  life  in  its  univerM] 
npf'^ts  — Medico- (Jhirttr^jical  Hcviev. 


Works  of  Uerbcri  Spencer  publuJud  by  D.  App  don  it  V«. 


ESSAYS: 

MORAL,  POLITICAL,  AND  ESTIIEriC. 

In  one  Voltime.    liargre  12mo.    386  pafrea. 

contests: 
I.  The  Philosophy  of  Style. 
II.  Ovcr-Lcfrislation. 

III.  Morals  of  Trade. 

IV.  Personal  Beauty. 

V.  Representative  Government 
VI.  Prison-Ethics. 

VII.  Railway  Morals  and  Railway  Policy. 
VIII.  Gracefulness. 
IX.  State  Tamperings  with  Money  and  Banks. 
X.  Reform  ;  the  Dangers  and  the  Safeguards. 


"  These  Kssays  form  a  new,  and  if  we  arc  not  misuiken,  a  most  popular  Lnstallmenl 
sf  the  intellectual  benefactions  of  that  earnest  writer  anil  profound  philosopher,  Her- 
bert Spencer.  There  ia  a  remarkaMo  union  of  the  speculative  and  practicil  in  thee* 
papers.  They  arc  the  fruit  of  studies  alike  economical  and  psychological;  they  touch 
the  problems  of  the  passing  hour,  and  they  grasp  truths  of  universal  application  ;  they 
will  be  founu  as  instructive  to  the  general  reader  as  interesting  to  political  and  3<icial 
et ude n t s." — JJoslon  Tra m«c ript. 

••These  Essays  exhibit  on  a;nQost  every  iia^re  the  powers  of  an  independent  human. 
Itiirian  thinker.  ^Ir.  Spencer's  ethics  are  rigid,  his  political  views  libenilistic,  and  hi* 
kim  is  the  production  ol  the  highest  eai-thly  good." — JletJiodUt  Quarterly  Jleview. 

"It  abounds  iij  the  results  of  the  sharp  observation,  the  wide  reach  of  ktnwledgei, 
and  the  capacity  to  write  clearly,  forcibly,  and  pointedly,  for  which  this  wiitef  Is  pre- 
eminent. The  subjects  are  all  such,as  concern  us  most  intimately,  and  they  are  treated 
with  admirable  tact  and  knowledge.  The  first  essay  on  the  Philosophy  of  Style  \t 
Worth  tlie  cost  of  the  volume;  it  would  be  a  deed  of  charity  to  print  It  by  itself^  and 
•end  it  to  the  editor  of  every  newsp.iper  in  the  land." — Keio  Eiigkinder. 

"Spencer  is  continually  gaining  ground  with  Americans;  he  makes  a  book  fbr  oil: 
more  serious  moods.  His  remarks  upon  legislation,  upon  the  nature  of  political  lu»ti- 
tutlons  and  of  their  fundamental  principles;  his  elucidation  of  those  foundation  trutli* 
wliich  control  the  policy  of  government,  are  of  peculiar  value  to  the  American  stii 
dcnV—IloKlon  Post. 

"ITiis  volume  will  receive  the  applause  of  every  serious  reader  tor  the  profound 
earnestness  and  thoroughness  with  which  its  views  arc  flaborated,  the  infinite  scientlfle 
knowledge  brought  to  bear  on  every  question,  and  the  acute  and  subtle  tblukjng  'U»- 
Vrtfcycd  In  every  chapter."— A'.  W.  Christian  Advocate. 

"A  more  In«tructivo,  suggestive,  and  stimulating  volume  has  net  r«acDed  on  t»  • 
Mn  tlmo." — PiociJence  Journiu. 


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